When it is known that something like four-fifths of the animal body consists of water, no argument will be necessary to prove the importance of a constant supply of the fluid in a proper condition for appropriation.
By the process of evaporation which is constantly going on from the skin, through the respiratory organs, and in other ways, water is constantly being excreted from the body, and when there is no supply from without to repair the loss, it must ultimately happen that all the animal tissues would become perfectly dried, which means that an animal weighing 100 lb. would be reduced to a mass weighing something under 30 lb. To compensate for the amount of water which is constantly being thrown off, even when in perfect rest, and to a much greater extent when undergoing exertion, it has been calculated that an adult man would require every twenty-four hours from ½ to 7/10 oz. of the fluid for each pound of his body weight. A man weighing 140 lb., therefore, will require from 70 to 90 oz. daily, and in ordinary English diet about 20 to 30 oz. of this is taken in the so-called solid food, and the remainder is drunk as liquid of some kind (Parkes). The horse, it is calculated, will require 8 to 12 gallons daily, a cow or small ox about 6 to 8 gallons, sheep or pigs ½ to 1 gallon (Parkes).
Colonel Fred. Smith states that from experiments made in 1866 the War Office fixed the daily supply for cavalry horses at 8 gallons, and artillery at 10 gallons per horse. This quantity, however, was to include all water used for stable purposes, and in the artillery was to include washing carriages. From Dr. Parkes's observation, however, this quantity would be quite insufficient, as he came to the conclusion that 16 gallons per day per horse for all purposes was not an excessive amount. Colonel Fred. Smith also remarks that in a stable of cavalry horses, doing very little work, and at a cool time of the year, the amount per horse was found to average 61/3 gallons; and from experiments which he made in India he found that during the month of February a horse consumed on an average 8½ gallons daily, which was made up as follows: Morning-water, 1.9 gallon; mid-day, 3-4 gallons; at evening, 3.15 gallons. It does not appear to have been ascertained how much water a horse would consume daily when water is kept constantly in the trough in the stable or box, but it is generally believed that a less quantity is taken than when the animal has the water supplied to him at intervals three times daily.
Granting that a very considerable quantity of water is absolutely essential to keep the animal organism in a perfectly healthy condition, it must also be allowed that it is quite as necessary to obtain pure water as it is to supply the system with pure food. The latter requirement can be complied with without much difficulty. The food of the horse is so simple in its character, and undergoes so little preparation, that a very moderate amount of care will secure the animal perfectly wholesome provender; but in the case of water the circumstances under which it is collected are so varied, and the sources of contamination are so numerous, that it is recognized by the experimental chemist as a fact beyond question, that when he requires pure water for scientific purposes he can only obtain it by the application of heat to convert the fluid into a vapour, which he is bound to convey through perfectly sterilized cold pipes, from which it will fall in the condition of water deprived of all foreign matter. In this condition of purity, however, it has lost all the flavour which makes it grateful to the palate, and at least certain products which are beneficial to the system. It becomes, therefore, most important to ascertain what impurities may be safely or advantageously admitted. Water in its absolutely pure condition consists of oxygen and hydrogen, and in this condition it may be obtained, theoretically, by the process of vaporizing under conditions which render contamination impossible. As it occurs, however, in seas and rivers, it holds in suspension or in solution various substances which it obtains from the earth and air through which it passes. Rain-water is sometimes referred to as the purest form in which water can be obtained naturally, but this implies that the rain shall fall and the water be collected in a place quite remote from habitations of all kinds, otherwise the various gases with which the atmosphere is charged, from the gaseous products of manufactures or living beings, are necessarily mixed with the falling rain, contaminating it sometimes to an extent which renders it poisonous or utterly unfit for use. Under ordinary conditions it is estimated that rain-water, even in rural districts, contains about 2 grains of solid matter to the gallon. In towns, particularly where large industries are carried on, the quantity of solids is necessarily much larger. The gases which contaminate rain-water are, in addition to carbonic acid, ammonia, sulphurous acid, and the emanations from drains and sewers. Other impurities are added as the rain passes over the roofs of buildings and along the gutters which are arranged for carrying it to the drains. Decaying vegetable and animal matters are frequently washed from the roofs of buildings, and when the water is carried along lead gutters, or stored in lead tanks, the sulphurous acid contained in the fluid, in addition to the products of decomposing vegetable matter, leads to the solution of the lead and renders the water poisonous, or at least highly injurious to the animals which drink it. When the water reaches the ground it becomes at once exposed to other sources of contamination. There is, first, the presence of putrefying substances on the surface, animal and vegetable, which leads to contamination with ammonia nitrates, nitrites, phosphates, and other constituents of natural and artificial manures, and in passing through the soil it meets with various soluble salts of lime, magnesia, and soda, all of which tend to make considerable modifications in the quality of the fluid, to what extent may he gathered from the analyses of several specimens of water which are given by Professor Axe, published in the fourth volume of the Royal Agricultural Society's Journal. December, 1893. Three samples will suffice, and it will be observed that the first one is most remarkable for the amount of solid constituents, especially common salt, which it contains. "At Woodhall Spa, in Lincolnshire, a water said to possess valuable medicinal properties yields no less than 1542.2 grains of saline matter per gallon, as follows: .