Generally, deep wells are safer from contamination than shallow wells, but may still, under certain circumstances, be polluted.
On the question whether a well which has been-polluted by a cesspool will become fit for use after the cesspool has been removed, no rule can be laid down. If the removal of the sources of pollution has been thorough, the well will frequently recover its purity; but under other circumstances the well may remain impure. As to the least distance between wells and cesspools compatible with safety, while the Local Government Board of London is content with 20-30 yards, Dr. Frankland insists on at least 200 yards. It would be more rational to forbid cesspools of all kinds; at the same time, possible leakages from drains, through injury or otherwise, must not be omitted from the estimate of risk of pollution. Again, the effect of increased demand upon the contents of the well at once extends the danger, because as the water in the well is lowered so is the area from which the well draws its supply increased, the ratio varying from 20 to 100 times the depression. Where a whole day’s supply is pumped at once into an elevated tank, the maximum figure will be reached.
Those who intend sinking wells are advised first to read a little book by Ernest Spon, on the ‘Present Practice of Sinking and Boring Wells,’ 2nd edition, 1885.
Rain-water collected from roofs forms a valuable auxiliary supply too often disregarded. In towns it is rarely pure enough for domestic use, but in country districts it is generally wholesome.
A country resident thus describes the manner in which he utilises rain-water, falling upon an ordinary tin roof, covered with some sort of metallic paint, said to contain no lead, and flowing into a large cemented brick cistern, whence it is pumped into the kitchen. The cistern differs from the usual construction in this manner: across the bottom, about 3 ft. nearer one side than the other, is excavated a trough or ditch about 2 ft. wide and 2 ft. deep; along the centre of this depression is built a brick wall from the bottom up to the top of the cistern, and having a few openings left through it at the very bottom. The whole cistern, bottom, sides, and canal included, is cemented as usual, excepting the division wall. Upon each side of the wall, at its base, 6-12 in. of charcoal is laid, and covered with well-washed stones to a further height of 6 in., merely to keep the charcoal from floating. The rain-water running from the roof into the larger division of the cistern, passes through the stone covering, the charcoal, the wall, the charcoal upon the other side, lastly, the stones, and is now ready for the pump placed in this smaller part. It is much better that the water at first pass into the larger division, as the filtration will be slower, and the cistern not so likely to overflow under a very heavy rainfall. He has used this cistern for many years, and was troubled only once, when some toads made their entrance at the top, which was just at the surface of the ground, soon making their presence known by a decided change in the flavour of the water.
If the house chances to be in a dusty situation, several plans will suggest themselves whereby a few gallons at the first of each rain may be prevented from entering the cistern. Should the house be small, and therefore the supply of water from its roof be limited, do not lessen the size of the cistern, but rather increase it, for with one of less capacity some of the supply must occasionally be allowed to go to waste during a wet time, and you will suffer in a drought, whereas a cistern that never overflows is the more to be relied upon in a long season without rain.
Rainfall varies exceedingly in different places, and even in the same situation it is impossible to foretell the amount to be expected during any short period of time, but the most careful observations show that about 4 ft. in depth descends at New York and vicinity every year, or nearly 1 in. a week. If this amount were to be furnished uniformly every week, the size of a cistern need only be sufficient to contain one week’s supply, but we often have periods of 4 weeks without receiving the average of one, and we must build accordingly.
The weekly average of 1 in. equals 1 cub. ft. upon every 12 ft. of surface, or3630 cub. ft. upon an acre, weighing about 113 tons. Upon a roof 40 ft. by 40 ft., 1600 sq. ft., it would be 133 cub. ft., 1037 gal., or about 26 barrels of 40 gal. each. A cistern 8 ft. across and 10 ft. deep would contain 502 cub. ft.; and one of 10 ft. across and 10 ft. deep, 785 cub. ft., or 6120 gal.—about the average fall upon a roof of the above size for 6 weeks; while the smaller cistern would hold 3900 gal., or a little less than 4 weeks’ rainfall. The weekly supply of 1037 gal. is equal to 148 gal. per day, or nearly 15 gal. to each individual of a family of 10. This is certainly enough, and more than enough, if used as it should be; but where water is plentiful it is wasted, and in our capricious climate, whether we depend upon wells or cisterns, it is wise to waste no water at all, at least during the warm summer months, and lay by not for a wet but a dry day. For this country, Field estimates 2-3 gallons of tank capacity for every square foot of roof area.
3. Rain-water Tank.
3. Rain-water Tank.
3. Rain-water Tank.
In Fig. 3a b c dshow the excavation that must be made for the cistern, and supposing the diagram to exhibit, as it does, a section of the cistern, the receptacle for the water will be, when finished, taking the relative proportions of the different parts into consideration, just about 9 ft. wide and 4½ ft. deep. Of course, the excavation must be made greater in breadth and depth than the dimensions given, to allow for the surrounding walls and the bottom. The walls may be of brick, cemented within, and backed with concrete or puddled clay without, or of monolithic concrete; but the bottom, in any case, should be made of concrete. The trenche f g hrunning across the bottom of the cistern is 2 ft. broad and 2 ft. deep. In the middle of this opening is built up a 9 in. brick wall, or a party-wall of concrete,i k. Along the bottom of the wall openingslare left at intervals. The party-wall divides the entire space into the larger outer cisternm, and the smaller inner cisternn. Supposing the breadth frometofto be 2 ft., and the wall 9 in., spaces of 7½ in. will be left on each side of the wall. These are filled to ¾ the height, or for 18 in., with lumps of charcoal, smooth pebbles, 1-3 in. in diameter, being laid along the top of the charcoal till the trench is filled up. The cistern is so constructed that the water from the roof entersm; it passes downwards through the stones and charcoal, as shown by the arrow atf, goes through the opening and forces its way upwards in the direction of the arrow ateinto the cisternn, in which it rises to the level of the water inm, to be drawn thence for use by a small pump.
Various modifications of this form of tank-filter will suggest themselves to readers possessing any mechanical genius. The great point is to prevent contamination from the soil by using good material and making sound work. Further, the overflow pipe of the tank must not communicate with any drain or sewer.
4. Rain-water Separator.
4. Rain-water Separator.
4. Rain-water Separator.
Recently several inventors have introduced apparatus for separating rain-water from impurities. One of these, bearing the name of Roberts, is illustrated in Fig. 4. Its principle of action is to reject the first portion of the rain which falls (as it is thiswhich chiefly washes the dirt off the roof), and only to collect the latter portion of the rain. The water from the roof first runs on to a strainer, that intercepts rubbish; it then passes through one of two channels in the upper part of the canter, balanced upon a pivot. At the commencement of a shower, the canter is raised in the position shown in Fig. 4, “running to waste,” and the bulk of the water passes through a channel which directs it into the lower or wastewater outlet. Meanwhile, a very small proportion of the water is accumulating in the lower part of the canter, very slowly in light rain but more rapidly in heavy rain, so that it is filled up by the time the roof has become clean. Then the weight of water causes it to fall down as shown in Fig. 4A“running to storage,” so that the clean water may run through the upper storage outlet pipe. This very useful little apparatus is made and sold by C. G. Roberts, Collards, Haslemere, Surrey.
4A. Rain-water Separator.
4A. Rain-water Separator.
4A. Rain-water Separator.
Perhaps this affords as good an opportunity as any of drawing attention to the highly artistic rain-water heads that have lately been introduced by Thomas Elsley, of 32 Great Portland Street, W. These are made to suit every style of architecture and every variety of roof and guttering, and practically without limit as to size. Their quality is beyond praise.
It is essential to bear in mind that rain-water is liable to exert considerable solvent action on lead, consequently pipes and cisterns of this metal must be avoided. The pipes may be of iron, or of specially lead-encased block-tin, and the cisterns of “galvanised” iron or slate.
As Eassie has pointed out, there is much to be considered in the arrangement of rain-water pipes from a sanitary point of view, where a separator and storage tank are not in use, because the foul air delivered from them is sucked into the rooms near the roof, on which the sun’s heat pours. A fire lighted in a room develops the same danger when the rain-water pipe terminates near the windows of the room. Another danger accruing from rain-water pipes which connect directly with the drain is due to the fact that the joints of the iron rain-water pipes are seldom air-tight, and foul air is therefore often driven or sucked into the rooms when the windows are open. It is easy to imagine how dangerous this must be in houses which have been fitted up with iron (or even lead) rain-water pipes running down the interior walls, and having their terminations close to a dormer window, skylight, or staircase ventilator on the roof, with the foot of the rain-water pipe taken direct into a drain leading to a town sewer. But the risk is greatly increased when the rain-water pipes are connected with a closed cesspool, to which the rain-water pipe is acting as a ventilator.
When rain-water pipes deliver into the drain directly, they are often made to act as soil pipes from the closets, in which case the evil is intensified. The soil from the closets is apt to adhere to the interior of the pipe, generally on the side opposite to that traversed by the rain-water, and the poisonous smell escapes at any bad joints and always at the roof orifice.
When the rain-water pipe is of cast iron, other sources of danger are present if the pipe is used also for conveying soil from a closet. Unless the rim of the soil pipe from the closet is joined to the rain-water pipe by a proper cast-iron socketed joint, the connection must be made by means of a piece of lead pipe which receives the soil pipe, and the joint between the lead soil pipe and the upper and lower parts of the cast-iron pipe cannot be properly soldered. Here sometimes grievous calamity follows cases where the combined pipe is ventilating the drain and sewer; the pipe joints are frequently open, and when the windows are unclosed for ventilation the foul air is whisked into thehouse. Eassie insists that it is cheaper to owner and dweller alike to have a separate soil-pipe erected at first.
5. Outlet of Rain-water Pipes.
5. Outlet of Rain-water Pipes.
5. Outlet of Rain-water Pipes.
All rain-water pipes should deliver into the open air, and have no connection with the drains, except when they are disconnected. They should discharge their contents over a gully grating as ata, Fig. 5, or underneath the grating as atb, the ends of the pipes in both cases being in the open air. Every householder should insist upon this being carried out. But occasionally the rain-water pipes descend inside the house and there is no open yard where a disconnecting gully can be fixed. In such a case a separate drain should be laid to the nearest area or yard, and separation ensured. In laying down new drains in a house, where the rain-water pipes must descend in the interior, it will be better to provide a separate or twin drain to the nearest open-air space.
Provision must be made at the roof for keeping foreign matters out of the rain-water pipes. Leaves, soot, and dirt will accumulate round the pipe orifices, and very often will cause the gutter to be flooded during a storm. The usual way to avert this is to fix over the opening of the pipe in the bottom of the gutter a galvanised open wire half-globe, or a raised cap of thick lead pierced with tolerably large holes. The cost for this is trifling, but the value is great. Whenever rain-water pipesmustrun down the inside wall of a house, lead should be adopted. Sometimes rain-water pipes are taken down in the interior, when a very little initial study could have brought them to the exterior face of a wall—where alone they should be taken, whenever it is possible to do so.
On attic roofs, and where only one side of the house can be used for the attachment of rain-water pipes, the water from one side is brought across the roof by means of a “box” gutter of wood, lined at the bottom and sides with lead or zinc, and covered with a board. This often emits a very foul smell, owing to the accumulation of decaying matter. When such guttering cannot be avoided, it should occasionally—say once a week—be carefully cleaned out. The same matters will sometimes silt up and stop the gullies, shown at the foot of the rain-water pipes (Fig. 5), hence it is equally necessary to see that these traps are cleaned out, say monthly.
Rain-water pipes are often made the waste pipes of lavatories, baths, sinks, and slop-pails. When properly disconnected at the foot, in the open air, and when the top of the rain-water pipe does not terminate under a window of an inhabited room, this does not much matter; but when the court-yard is limited in area, and there is a window belonging to a living or sleeping room just overhead, where the rain from the roof delivers itself into the upright pipe, an offence will arise from the decomposing fats of soap, which form a slimy mess adhering to the interior of the pipe, that no amount of rainfall will dislodge.
Cisterns.—Cisterns should be in a cistern-room if possible, but, at all events, placed where they can be got at, covered over with suitable fittings, and ventilated to the open air. A drinking-water cistern should never be placed in a water-closet, for no amount of disconnection in such a case will suffice to counteract its evil surroundings. Neither should it be placed in a bath-room, which is liable to a steam-laden atmosphere. Nothing can be said against a site out of doors, on the flats, or below (if away from dustbins and ash-heaps); but in such cases the cistern, with its service pipes, should bewell protected from frost. The position of a cistern should be equally carefully chosen no matter whether the supply be constant or intermittent, or whether there be a high or a low pressure cistern. And not only should it be made certain that the “standing waste” pipe of the cistern delivers in the open air, but that any “overflow” pipe of the cistern delivers in like cleanly fashion. It is too common to take these wastes down to the nearest sink. It might prove expedient to thus disconnect a cistern waste when time presses, and when the alternative is costly, but the practice is not to be commended.
Eassie’s strictures with regard to cisterns apply equally to those feed cisterns which supply hot-water circulating cisterns or boilers where water is heated for kitchen, scullery, still-room, or bath-room uses. It is too common to find the feed cistern, which is the small iron cistern that automatically keeps the kitchen or other basement boiler full, placed in the darkest corner of the commonest stowaway cupboard, with its overflow pipe joined to the drain.
The materials of which cisterns are constructed vary much in town and country. In old houses will be frequently found cisterns formed of slabs of stone, just as they have been raised from the quarry, and sometimes of slabs of rough slate, and than these, provided they are regularly cleaned out and the waste pipes disconnected, probably no better basement cistern could be found. The same might perhaps be said of brickwork cemented inside. Cisterns composed of slate possess a drawback in their weight, which sometimes prevents them from being adopted upstairs. It has become a frequent practice now to have them enamelled white inside, so that the slightest discoloration of the water, or sediment at the bottom, can be instantly detected.
Cisterns composed of metal throughout embrace old cisterns of cast lead, dated early in the 18th century; these are quite harmless, on account of their natural silver alloy, and they may be trusted, all other conditions being satisfactory. Cast-iron cisterns, made of plates bolted together, if kept full, and not subject to rust, are unobjectionable. Wrought iron, which has afterwards been “galvanised,” is a very common form of cistern, and appears to be the cheapest. Little can be said in its disfavour, although experiments made in America have proved that some waters attack the inner coating. The commonest form of cistern is composed of wooden framing lined inside with sheet lead. This is not the best for storing drinking-water, and slate would be preferable; but no one would say that all water drawn from leaden cisterns would injuriously affect health. The interior of a lead-lined cistern will be found to acquire a whitish coating, and it is due to this chemical alteration of its surface that the contained water can be drunk with more or less impunity. Nevertheless, there are some waters which very readily attack lead, and care should be exercised in this respect. In cleaning out a lead cistern the surface should never be scraped, but simply washed down with a moderately hard brush. Sometimes houses are provided with zinc-lined wooden cisterns; this metal for several reasons is one of the worst materials for water storage, and should never be used for drinking-water. Neither should wooden butts or barrels be employed for storing water anywhere in a house, as they speedily become lined with a low vegetable growth detrimental to health.
A great mistake consists in storing away a great quantity of water in abnormally large cisterns, in consequence of which the tap is drawing off for a very long period the water first delivered to it, and which is not the cleanest water. This does not so much matter in cisterns which supply closets or baths, but it is reprehensible when the water is for the bedroom decanter and the nursery.
Pipes.—Pipes for conveying water are generally of lead, because it is more easily bent than any other metal; but frequently iron pipes are substituted when the water main has to be brought from a great distance. Eassie remarks that the conveyance of some waters in long lengths of leaden pipe, in which the water must necessarily stand, and the use of leaden suction pipes in wells, is not a thing to be looked upon with great favour. Hence it is that galvanised iron pipes are used by some, and in the case ofwater conveyance from a long distance, the cast-iron pipes coated inside with Dr. Angus Smith’s solution, or subjected to the Bower-Barff system of protection against rust, are now very largely adopted. Glass-lined pipes of the American pattern have also been introduced into this country, but have not yet made much headway, which is a pity, seeing that glass forms the best of all conduits for water. Much depends upon whether the water is of such a character as to rapidly decompose lead.
Leaden pipes, of sufficient weight per lineal foot, may fitly conduct the flushing water for closets and the cold water to baths and lavatories; but what is called “lead-encased block-tin pipe” should be used in conveying water from the separate drinking-water cistern. The cost is some 50 per cent. more than for leaden pipe, and there is more difficulty in making the joints, but these points are overbalanced by the certainty of non-pollution of the water. Water pipes should be fixed in separate wall chases, easy of access. Service pipes should also be kept separate from each other, and provided with proper stop-cocks in case of accident.
Pumps.—It will not be out of place here to offer a few remarks on the construction, capacity, and working of the 3 kinds of common pump in everyday use—i.e. (1) the lift-pump; for wells not over 30 ft. deep, (2) the lift and force, for wells under 30 ft. deep, but forcing the water to the top of the house, and (3) the lift and force, for wells 30-300 ft. deep.
The working capacity of a pump is governed by the atmospheric pressure, which roughly averages 15 lb. per sq. in. It is also necessary to remember that 1 gal. of water weighs 10 lb. The quantity of water a pump will deliver per hour depends on the size of the working barrel, the number of strokes, and the length of the stroke. Thus, if the barrel is 4 in. diam., with a 10 in. stroke, piston working 30 times a minute, then the rule is—square the diameter of the barrel and multiply it by the length of stroke, the number of strokes per minute, and the number of minutes per hour, and divide by 353, thus:—
42 in. × 10 in. stroke × 30 strokes × 60 minutes
353
= 815 gal. per hour. About 10 per cent. is deducted for loss. The horse-power required is the number of lb. of water delivered per minute, multiplied by the height raised in ft., and divided by 33,000. Thus:—
815 gal. × 10 lb. × 30 ft. lift= 7·4 H.P.
33,000
6. Lift Pump.
6. Lift Pump.
6. Lift Pump.
Fig. 6 shows a vertical section of the simple lift-pump.ais the working barrel, bored true, to enable the piston or bucketbto move up and down, air-tight. The usual length of barrel in a common pump is 10 in. and the diameters are 2, 2½, 3, 3½, 4, 5, and 6 in.; a 3 in. barrel is called a 3 in. pump. The stroke is the length of the barrel; but a crank, 5 in. projection from the centre of a shaft, will give a 10 in. stroke at one revolution; but in the common pump shown, use is made of a lever pump handle, whose short armc dis about 6 in. long, and the long arm or handled eis usually 36 in., making the power as 6 to 1;fis the fulcrum or prop. Improved pumps have a joint atf, which causes the piston to work in a perpendicular line, instead of grinding against the side of the barrel. The headgof the pump is made a little larger than the barrel, to enable the piston to pass freely to the barrel cylinder; in wrought-iron pumps, the nozzle is riveted to the heads, and unless the head is larger than the barrel these rivets would prevent the piston from passing, and injure the leather packing on the bucket. The nozzleh, fixed at the lower part of head, is to run off the water at each rise of the piston. There is 1 valveiat the bottom of the barrel, and another in the bucketb.
The suction pipekshould be ⅔ the diameter of the pump barrel. A roselis fixed at the end of the suction pipe to keep out any solid matter that might be drawn into the pump and stop the action of the valves. The suction pipe must be fixed with great care.The joints must be air-tight: if of cast flange-pipe, which is the most durable, a packing of hemp, with white and red lead, and screwed up with 4 nuts and screws, or a washer of vulcanised rubber ⅜ in. thick, with screw bolts, is best. If the suction pipe is of gas-tube, the sockets must all be taken off, and a paint of boiled oil and red-lead be put on the screwed end, then a string of raw hemp bound round and well screwed up with the gas tongs, making a sure joint for cold water, steam, or gas.
Many plumbers prefer lead pipe, so that they can make the usual plumbers’ joint. The tailmof the pump is for fixing the suction pipe on a plank level with the ground. Stagesnare fixed at every 12 ft. in a well; the suction pipe is fixed to these by a strap staple, or the action of the pump would damage the joints. There are two plans for fixing the suction pipe; (1) in a wellodirectly under the pump; (2) the suction pipepmay be laid in a horizontal direction, and about 18 in. deep under the ground (to keep the water from freezing in winter) for almost any distance to a pond, the only consideration being the extra labour of exhausting so much air. In the end of such suction pipepit is usual to fix an extra valve, called a “tail” valve, to prevent the water from running out of the pipe when not in use. The action is simply explained. First raise the handlee, which lowers the pistonbtoi; during this movement the air that was in the barrelais forced through the valve in the pistonb; when the handle is lowered, and the piston begins to rise, this valve closes and pumps out the air; in the meantime the air expands in the suction pipek, and rises into the barrelbthrough the valvei; at the second stroke of the piston this valve closes and prevents the air getting back to the suction pipe, which is pumped out as before. After a few strokes of the pump handle, the air in the suction pipe is nearly drawn out, creating what is called a vacuum, and then as the water is pressed by the outward air equal to 15 lb. on the sq. in., the water rises into the barrel as fast as the piston rises: also the water will remain in the suction pipe as long as the piston and valves are in proper working order.
The following table of dimensions for hand-worked simple lift-pumps will be found useful:—
Height for Water to be raised.Diam. of Pump Barrel.Water delivered per Hour at 30 Strokes per Min.Diam. of Suction Pipe.Thickness of Well Rods for Deep Wells.ft.in.gal.in.in.1461640412051110313047322½⅞403½5552½¾5034122¾752½2602⅝10021831½⅝
7. Lift and Force Pump. 8. Deep-well Pump.
7. Lift and Force Pump. 8. Deep-well Pump.
7. Lift and Force Pump. 8. Deep-well Pump.
Fig. 7 shows a lift- and force-pump suitable for raising water from a well 30 ft. deep, and forcing it to the top of a house. The pump barrelais fixed to a strong plankb, and fitted with “slings” atcto enable the piston to work parallel in the barrel, a guide rod working through a collar guiding the piston in a perpendicular position,dis the handle. The suction pipeeand rosefare fixed in the wellgas already explained. At the top of the working barrel is a stuffing-boxh, filled with hemp and tallow, which keeps the pump rod water-tight. When the piston is raised to the top of the barrel, the valveiin the delivery pipekcloses, and prevents the water descending at the down-stroke of the piston. The valve in the bucketl, also atmin the barrela, is the same as in the common pump. The pipekis called the “force” for this description of pump.
Fig. 8 shows a design for a deep-well pump, consisting of the usual fittings—viz. a brass barrela, a suction pipe with roseb, rising main pipec, well-rodd, wooden or iron stagese f g, and clip and guide pulleysh. The well-rod and the rising main must be well secured to the stages, which are fixed every 12 ft. down the well. An extra strong stage is fixed ati, to carry the pump—if of wood, beech or ash, 5 ft. × 9 in. × 4 in.; the other stages may be 4 in. sq.
The handle is mounted on a plankkfitted with guide slings, either at right angles or sideways to the plank. The handlelis weighted with a solid ball-end atm, which will balance the well-rod fixed to the piston. By fixing the pump barrel down the well about 12 ft. from the level of the water, the pump will act better than if it were fixed 30 ft. above the water, because any small wear and tear of the piston does not so soon affect the action of the pump, and therefore saves trouble and expense, as the pump will keep in working order longer. It is usual to fix an air-vessel atn. The valvesoare similar to those already described. In the best-constructed pumps, man-holes are arranged near the valves to enable workmen to clean or repair the same, without taking up the pump. Every care should be given to make strong and sound joints for the suction pipe and delivery pipe, as the pump cannot do its proper duty should the pipes be leaky or draw air.
To find the total weight or pressure of water to be raised from a well, reckon fromthe water level in the well to the delivery in the house tank or elsewhere. For example, if the well is 27 ft. deep, and the house tank is 50 ft. above the pump barrel; then you have 77 ft. pressure, or about 39 lb. pressure per sq. in. That portion of the pipe which takes a horizontal position may be neglected. The pressure of water in working a pump is according to the diameter of the pump barrel. Suppose the barrel to be 3 in. diam., it would contain 7 sq. in., and say the total height of water raised to be 77 ft., equal to 39 lb. pressure, multiplied by 7 sq. in., is equal to 539 lb. to be raised or balanced by a pump handle; then if the leverage of the pump handle were, the short arm 6 in. and long arm 36 in., or as 6 to 1, you have (539 × 1) ÷ 56 = 90 lb. power on the handle to work the pump, which would require 2 men to do the work, unless you obtained extra leverage by wheel work. When the suction or delivery pipe is too small, it adds enormously to the power required to work a pump, and the water is then called “wiredrawn.” When pumps are required for tar or liquid manure, the suction and delivery pipe should be the same size as the pump barrel, to prevent choking.
The operations of plumbing and making joints in pipes will be found fully described and illustrated in ‘Spons’ Mechanics’ Own Book’; and many other methods of raising water for household and agricultural purposes are explained in ‘Workshop Receipts,’ 4th series.
Purification.—At a recent meeting of the Institution of Civil Engineers, Prof. Frankland read a paper dealing with the question of water purification, in which he remarked that the earliest attempts to purify water dealt simply with the removal of visible suspended particles; but later, chemists have turned their attention to the matters present in solution in water. Since the advance of the germ theory of disease, and the known fact that living organisms were the cause of some, and probably of all, zymotic diseases, the demand for a test which should recognise the absence or presence of micro-organisms in water had become imperative. It was, however, only during the last few years that any such test had been set forth, and this was owing to Dr. Koch, of Berlin. By this means the only great step which had been made since the last Rivers Pollution Commission had been achieved. It had been supposed that most filtering materials offered little or no barrier to micro-organisms; but it was now known that many substances had this power to a greater or less degree. It had also been found that, in order to continue their efficiency, frequent renewal of the filtering material was necessary.
Vegetable carbon employed in the form of charcoal or coke was found to occupy a high place as a biological filter, although previously, owing to its chemical inactivity, it had been disregarded. Being an inexpensive material, and easily renewed, it was destined to be of great service in the purification of water. Experiments were also made by the agitation of water with solid particles. It was found that very porous substances, like coke, animal and vegetable charcoal, were highly efficient in removing organised matter from water when the latter came in contact with them in this manner. Also, it was found that the well-known precipitation process, introduced by Dr. Clark, for softening water with lime, had a most marked effect in removing micro-organisms from water. In the case of water softened by this process, it was found that a reduction of 98 per cent. in the number of micro-organisms was effected, the chemical improvement being comparatively insignificant.
Water which had been subjected to an exhaustive process of natural filtration had been found to be almost free from micro-organisms. Thus, the deep-well water obtained from the chalk near London contained as few as eight organisms per cubic centimetre, whereas samples of river water from the Thames, Lea, and Wey had been known to contain as many thousands.
The same well-known authority on water published the following statements in theNineteenth Century. He described the subject of domestic filtration as one which, in a town with a water supply like that of London, possesses peculiar interest, and is of nolittle importance. Most people imagine that by once going to the expense of a filter they have secured for themselves a safeguard which will endure throughout all time without further trouble. No mistake could be greater, for without preserving constant watchfulness, and bestowing great care upon domestic filtration, it is probable that the process will not only entirely fail to purify the water, but will actually render it more impure than before. For the accumulation of putrescent organic matter upon and within the filtering material furnishes a favourable nest for the development of minute worms and other disgusting organisms, which not unfrequently pervade the filtered water; whilst the proportion of organic matter in the effluent water is often considerably greater than that present before filtration.
Of the substances in general use for the household filtration of water, spongy iron and animal charcoal take the first place. Both these substances possess the property of removing a very large proportion of the organic matter present in water. They both, in the first instance, possess this purifying power to about an equal extent; but whereas the animal charcoal very soon loses its power, the spongy iron retains its efficacy unimpaired for a much longer time. Indeed, in spongy iron we possess the most valuable of all known materials for filtration, inasmuch as, besides removing such a large proportion of organic matter from water, it has been found to be absolutely fatal to bacterial life, and thus acts as an invaluable safeguard against the propagation of disease through drinking-water.
It is satisfactory to learn that in countries where the results of scientific research more rapidly receive practical application than is unfortunately the case amongst us, spongy iron is actually being employed on the large scale for filtration where only a very impure source of water supply is procurable. This refers to the recent introduction of spongy-iron filter beds at the Antwerp waterworks. It would be very desirable that such filter beds should be adopted by the London water companies until they shall abandon the present impure source of supply.
Animal charcoal, on the other hand, far from being fatal to the lower forms of life, is highly favourable to their development and growth; in fact, in the water drawn from a charcoal filter which has not been renewed sufficiently often, myriads of minute worms may frequently be found.
Thus spongy iron enables those who can afford the expense to obtain pure drinking-water even from an impure source; but this should not deter those interested in the public health from using their influence to obtain a water supply which requires no domestic filtration, and shall be equally bright and healthful for both rich and poor.
In a publication by Prof. Koch (Med. Wochenschrift, 1885, No. 37) on the scope of the bacteriological examination of water, it is asserted that a large proportion of micro-organisms proves that the water has received putrescent admixtures, charged with micro-organisms, impure affluxes, &c., which may convey, along with many harmless micro-organisms, also pathogenous kinds, i.e. infectious matters. Further, that as far as present observations extend, the number of micro-organisms in good waters ranges from 10 to 150 germs capable of development per c.c. As soon as the number of germs decidedly exceeds this number the water may be suspected of having received affluents. If the number reaches or exceeds 1000 per c.c., such water should not be admitted for drinking, at least in time of a cholera epidemic.
Dr. Link has lately examined a great number of the Dantzig well-waters chemically and bacterioscopically. The results obtained agree, however, very ill with the above opinions of Koch. On the contrary, it appears very plainly that regular relations between the chemical results and those of the bacterioscopic examination do not obtain. Many well-waters, chemically good and not directly or indirectly accessible to animal pollutions, often contained considerable numbers of microbia, whilst other waters, chemically bad and evidently contaminated by the influx of sewage, showed very small numbers of bacteria undergoing development. If we further consider that, by far the majority,indeed, as a rule the totality of the bacteria contained in well-water, are indubitably of a harmless nature, and that when a pollution of the water by pathogenous germs has actually occurred, such germs will not in general find the conditions necessary for their increase, especially a temperature approximating to that of the body and a sufficient concentration of nutritive matter, but that they will rather perish from the overgrowth of the other bacteria inhabiting the water, we shall see that a judgment on the quality of water—according to the results of a bacterioscopic examination extending merely to a determination of the number of germs capable of development—must lead to inaccurate conclusions, which contradict the results of chemical analysis.
The attempt to put forward bacterioscopic examination as a decisive criterion for the character of a water is therefore devoid of a satisfactory basis. For the present, Dr. Link thinks the decision must be left to chemical analysis.
At any rate it is doubtful whether the test of the number of micro-organisms should determine the question whether a water is or is not safe to drink. Dr. Koch’s gelatine peptone test has enabled the analyst to recognise the absence or presence of microphytes; but, as was stated at a recent meeting of the Society of Medical Officers of Health, a sample of river water which might be marked “very good” by this test would develop an enormous number of colonies if kept for a few days, even in a “sterilised flask” protected from aerial infection. Prof. G. Bischof says, in fact, that a sample of New River water kept for six days in the above manner compares unfavourably as regards the number of “colonies” with a sample taken from the company’s main and polluted with one per cent. of sewage, or with a sample of Thames water taken at London Bridge. It seems certain too that the water stored on board ship must develop an enormous number of “colonies”; but no special amount of disease is attributable to them, and it would seem to follow that, unless the number of microphytes can be shown to indicate, or to be a measure of, pollution, Koch’s test is of little utility except as a guide to waterworks’ engineers, by pointing out that the filters want cleaning. In the laboratory the test is no doubt of considerable value; but in analysing water it must be applied with discrimination, and waters of a totally different character should not be compared by the number of organisms. For instance, the water from Loch Katrine might contain large numbers of micro-organisms, and yet be perfectly safe as compared with a water in which few microphytes could be found, but which had been accidentally polluted by some of those pathogenous germs which undoubtedly exist, and which produce disease when they find a suitable environment. Not until we are able to discriminate between the harmless and the disease-producing microphytes, shall we be able to test a water supply and declare it practically pure.
The foregoing paragraphs will suffice to show what a very unsatisfactory state our present knowledge of water is in. The only useful fact to be deduced from all the argument is that every household should filter its own drinking-water and take care that the filters are always kept clean and in good working order. There is one simple test for the purity of water, introduced by Dr. Hager in 1871, consisting of a tannin solution, directions for which will be found in the Housekeeper’s section. It remains to notice the chief kinds of filter.
Filtration is destined to perform three distinct functions, at least where the water is required for domestic use; these are (1) to remove suspended impurities; (2) to remove a portion of the impurities in solution, and (3) to destroy and remove low organic bodies.
The first step is efficiently performed by nature, in the case of well and spring water, by subsidence and a long period of filtration through the earth; in the case of river water supplied by the various companies, it is carried out in immense settling ponds and filter beds of sand and gravel. This suffices for water destined for many purposes. The second and third steps are essential for all drinking-water, and are the aim of every domestic filter. The construction of water filters may now be discussed according to the nature of the filtering medium.
Gravel and Sand.—The usual plan adopted by the water companies is to build a series of tunnels with bricks without mortar; these are covered with a layer of fine gravel 2 ft. thick, then a stratum of fine gravel and coarse sand, and lastly a layer of 2 ft. of fine sand. The water is first pumped into a reservoir, and after a time, for the subsidence of the coarser impurities, the water flows through the filter beds, which are slightly lower. For the benefit of those desirous of filtering water on a large scale with sand filtering beds, it may be stated that there should be 1½ yd. of filtering area for each 1000 gal. per day. For effective work, the descent of the water should not exceed 6 in. per hour.
This simple means of arresting solid impurities and an appreciable portion of the matters in solution, may be applied on a domestic scale, in the following manner.
Procure an ordinary wooden pail and bore a number of ¼ in. holes all over the bottom. Next prepare a fine muslin bag, a little larger than the bottom of the pail, and about 1 in. in height. The bag is now filled with clean, well-washed sand, and placed in the pail. Water is next poured in, and the edges of the bag are pressed against the sides of the pail. Such a filter was tested by mixing a dry sienna colour in a gallon of water, and, passing through, the colour was so fine as to be an impalpable powder, rendering the water a deep chocolate colour. On pouring this mixture on to the filter pad and collecting the water, it was found free of all colouring matter. This was a very satisfactory test for such a simple appliance, and the latter cannot be too strongly recommended in cases where a more complicated arrangement cannot be substituted. The finest and cleanest sand is desirable, such as that to be purchased at glass manufactories.
This filter, however, at its best, is but a good strainer, and will only arrest the suspended particles. In a modern filter more perfect work is required, and another effect produced, in order that water containing objectionable matter in solution should be rendered fit for drinking purposes. Many persons when they see a water quite clear imagine that it must be in a good state for drinking. They should remember, however, that many substances which entirely dissolve in water do not diminish its clearness. Hence a clear, bright water may, despite its clearness, be charged with a poison or substances more or less injurious to health; such, for instance, as soluble animal matter.
To make a perfect filter, which should have the double action of arresting the finest suspended matter and removing the matters held in solution, and the whole to cost but little and capable of being made by any housewife, has long been an object of much attention, and, after many experiments and testing various substances in many combinations, the following plan is suggested as giving very perfect results, and costing only about 8s.
Purchase a common galvanised iron pail, which costs 2s.Take it to a tin-shop and have a hole cut in the centre of the bottom about ¼ in. diameter, and direct the workman to solder around it a piece of tin about ¾ in. deep, to form a spout to direct the flow of water downward in a uniform direction. Obtain about 2 qt. of small stones, and, after a good washing, place about 2 in. of these at bottom of pail to form a drain.
On this lay a partition of horse-hair cloth or Canton flannel cut to size of pail. On this spread a layer of animal charcoal, sold by wholesale chemists as boneblack at about 5d.a lb. Select this about the size of gunpowder grains, and not in powder. This layer should be 3 or 4 in. A second partition having been placed, add 3 in. of sand, as clean and as fine as possible. Those within reach of glassmakers should purchase the sand there, as it is only with that quality of sand that the best results can be obtained. On this place another partition, and add more fine stones or shingle—say for 2 or 3 in. This serves as a weight to keep the upper partition in place, and completes the filter. By allowing the filtration to proceed in an upward instead of a downward direction much better results are obtained.
Charcoal, simple.—All kinds of charcoal, but especially animal charcoal, are useful in the construction of filters, and have consequently been much used for that purpose. Charcoal, as is well known, is a powerful decolorising agent, and possesses the property in a remarkable degree of abstracting organic matter, organic colouring principles, and gaseous odours from water and other liquids. It has been shown that it deprives liquids, for example, of their bitter principles, of alkaloids, of resins, and even of metallic salts, so that its usefulness as a medium through which to pass any suspected water is undoubted. The one point to be observed is that it does not retain its purifying power for any great length of time, so that any filter depending upon it for its purifying principle must either be renewed or the power of the charcoal restored from time to time, and this the more frequently in proportion to the amount of impurity present in the water. A combination filter of sand or gravel and granulated charcoal is a good one; but the physical, or chemico-physical, action of such compound filters, or of the other well-known filter, composed of a solid porous carbon mass, differ in no respect from that of the simple substances composing them; that is to say, such combinations or arrangements are much more a matter of fancy or convenience than of increased efficiency.
Experiments on the filtration of water through animal charcoal were made on the New River Company’s supply in the year 1866, and they showed that a large proportion of the organic matter was removed from the water. These experiments were afterwards repeated, in 1870, with Thames water supplied in London, which contains a much larger proportion of organic matter, and in this case also the animal charcoal removed a large proportion of the impurity. In continuing the use of the filter with Thames water, however, it became evident that the polluting matter removed from the water was only stored up in the pores of the charcoal, for, after the lapse of a few months, it developed vast numbers of animalcula, which passed out of the filter with the water, rendering the latter more impure than it was before filtration. Prof. Frankland reported in 1874 on these experiments as follows:—“Myriads of minute worms were developed in the animal charcoal, and passed out with the water, when these filters were used for Thames water, and when the charcoal was not renewed at sufficiently short intervals. The property which animal charcoal possesses in a high degree, of favouring the growth of the low forms of organic life, is a serious drawback to its use as a filtering medium for potable waters. Animal charcoal can only be used with safety for waters of considerable initial purity; and even when so used, it is essential that it should be renovated at frequent intervals, not by mere washing, but by actual ignition in a close vessel. Indeed, sufficiently frequent renovation of the filtering medium is an absolutely essential condition in all filters.”