Waters containing much lime are often bright and aparkling to the eye and agreeably sweet to the taste. They become somewhat milky when boiled, and leave a sediment which encrusts the inaide of kettlea or boilers. When strongly impregnated with lime, they will even deposit a calcareous coating along their channels aa they flow in the open air, or will petrify, as it ia termed, any substancea immeraed in them. These circumstances are due to the fact that the lime ia held in aolution in the water by the help of free, dissolved carbonic acid gas, and when thia gas ia permitted to eacape, or driven off by boiling, the lime ean no longer be retained in solution, and it is accordingly deposited. Hard waters, therefore, are generally made much aofter and purer by boiling. lf, however, much lime be present in the atate of aulphate, mere boiling will not aoften it, but if a little aoda be added during the boiling, the sulphate will be decomposed and readily separated. A good and cheap method of softening hard waters is now beiog carried out by several of the largeat Engliah water Companies. It ia known as " Clark's process," and conaista in adding lime water to the water already containing lime. The lime added combines with the excess of carbonic acid gas, which holda in aolution the lime present in the water, and the latter portion, and alao the newly formed carbonate, are precipitated to the bottom of tho tank or reservoir.
It will thus be aeen that the water which collects in hilly districts and flows in streams and rivers through all kinda of country and over many different rocka and aoila may, and generally does, contain organio and saline matters both in solution and in suspension. It is not, therefore, to be recommended for drinking purpoaes until it has been auftened and filtered. • Spring and well water ia that which falls upon and filters through porous rocks. Owing to the carbonic aoht which it contains, it dissolvea a large quantity of aaline matter as it filters through the different atrata. In its downward course, Ulla water aooner or later reaches a stratum which it cannot permeate, and is hence brought to a atand. If, however, the atratum happen to lie on an inclined plane, the water runs along it, and eventually issues from the earth where the rock crops out. It is iu this manner that all springs and wells are formed, the latter being constructed by digging through aeveral atrata until one is reached upon which water is atanding, or over which water is flowing.
As we have already seen, the solvent properties of water enable it to take up many aubatances from the rocks and wails through which it pasaea, and it often happens that in the neighbourhood of dwellings and farnayards, aud especially in towns, the water of shallow wells becomes very impure, and conaequently unwholesome to drink. The raina that fall upon the filth accumulated in towns waah out tho soluble substances it contains. carry them into the soil, and through this, by degrees, to the walla by which the wants of the inhabitants are aupplied. Thia has often been productive of aelious and fatal disease. Hence arises the necessity of preventing, aa far as posaible, the accumulation of refuse, and, when such accumulation ia unavoidable, of placing it at the greatest posaible distance from wella which yield water for daily use. And hence, also, the advisability of brioging water from a distance for the aupply of large towns.
The proximity of graveyards to wells and aprings from which drinking water is obtained is still more liable to render the water unwholesome by charging it with all kinds of objectionable matter. Water from a well standing close to an old churchyard in the neighbourhood of London, and analyzed by Noad, was found to contain the enormous quantity of 100 grains of solid matter per gallon, more than half of this consisting of nitrates of lime and magnesia. The presence of these salts in auch quantity could only be traced to the proximity of the graveyard, as they are invariably produced by the decay of animal mattera in porous soila. Well water frequently contains vegetable matter also, and of a kind which renders it wholly unfit for drinkiog purposes. In sandy districts, the decaying vegetable rnatters of the aurface•soil are observed to sink down and form a thin yellow layer in the aubaoil, which is impervious to water. Being arreated by this layer, the rain water, while resting upon it, takes up a certain quantity of the vegetable matter ; and when collected in wells, it is often dark-coloured, marshy in taste and smell, and very unwholesome. Purification of such water may he effeeted by filtering it through charcoal, or by putting chips of oak wood into it. Or it may be boiled, thus causing the organic matter to coagulate, as it were, and to collect in flocks, when the water cools, leaving it wholesome and nearly free from taste and smell. This property of being coagulated by boiling, and by the tannin contained in oak wood, show that the organic matter in water is of an albuminous character, or resembles white of egg. By coagulating, the organic substances not only fall themselves, but carry down other matter, thus completely clarifying or purifying the water.
The sources from which country villages are supplied with drinking water are almoet always shallow wells, each house or cottage having its own. As a rule, no care is taken to prevent the water in these wells from being contaminated with fonl organic refuee, and hence it is rarely fit for drinking purposes, In some eases, manure heaps, pigstyes, and even cesspools, are permitted to remain in close proximity to the well which supplies whole families with water for drinking, cookiug, and other purposes. Water from such wells is not only unfitted for consumption, but, from a sanitary point of view, absolutely dangerous. If it be impossible to avoid the contamination of the water in these wells, the best and safest plan to adopt in villages would be to establish one large deep well for the supply of the whole, placed in such a position as to be readily accessible and yet far removed from all chance of pollution with sewage and other injurious foreign matter. In the larger villages and towns, the supply is obtained either from such deep wells or from a neighbouring stream or lake, the water being purified sometimes by filtration through a bed of sand or gravel, and then condueted by means of underground pipes to the different streets and houses. Water thus supplied is, of course, much more wholesome than that obtained from shallow wells, but it is well never to use it for driuking purposes without careful filtration through a carbon filter, in order that any accidental impurity taken up in the underground pipes may be removed.