WATER SUPPLY

in a scientific sense, is a problem connected only with towns or closely populated regions. and undeveloped regions, natural sources such as springs or streams are relied on, and purity is sufficiently a ured, except when storage is nece ary on account of recurring drought. To save portage wells have always been and still are in common use. These may be cla ified as dipping and draw wells in the majorty of cases, and it may be noted that they are the most dangerous, as well as containing the hardest water. If the water table lies at a fair depth from the surface they may be looked upon as stores of filtered water. They are obviously open to pollution from surface water off manured lands and other sources; organic matter, ammonia, nitrates, chlorium, and even nitrites are common impurities. Draw wells may be considered to reach a depth of 20 ft. Both types are to be condemned as drawing their water from surface areas overlying impervious strata. Deep wells are those containing water from below such strata, and usually from a distance. They may be quite satisfactory, particularly if properly enclosed at the surface and drawn by means of a pump. Artesian wells form one of the best sources of supply and in the colonies as well as in towns in the old countries they are he coming much more numerous. Such waters are obtained from a great distance, usually upland, and below several layers of impervious strata; they are therefore of great purity except when brackish or salt or warm. ‘They are, however, free from organic matter, though the water is often objectionably hard. Cheaper than any of these comes the American type of windmill, but arrangement for storage is generally a somewhat added cost. Where pipes lead from the pump to tanks, the former should be of cast iron, with spigot and socket ends and joints of yarn and blue lead; tank are usually of cast or wrought iron and galvanized, but special paint should be applied in addition. The bydraulic ram ds largely in use for supplying water from streams and ponds; it is automatic, durable, and extremely economical. City Supply—When the supply required is large and the district extensive and uneven larger provision than that of wells is nece ary. The water may he taken by means of pumps from a river near by, or obtained from a distance, usually an upland surface region. In such cases provision must be made for pre ure in order to supply not only the upper stories of houses, but also houses situated on elevated sites. This may be developed by force pumps which supply water to a tower situated above the highest part of the supply pipes. Such 2 tower maintains a constant ‘head’ of water and gives pre ure if the pumps are intermittently worked; a reservoir may be constructed at such a height for storage and pre ure. Such arrangements are becoming le common, reliance being placed entirely on pumping. Gravitation may be used for giving pre ure when the water is drawn from up upland surface regions, storage tanks being arranged in the course of the system at convenient and _ sufficient heights. In such a system, such as is being adopted steadily by larger industrial areas. Intakes—Valve towers are erected in reservoirs and lakes; in the case of rivers, the supply may be brought by a parallel channel from upper reaches to a lateral reservoir; more often tunnels are built in a masonry wall, which lead to the reservoir; sometimes a natural or artificial portion of the bank forms 2 first filter bed, the water being allowed to percolate through. If the head waters are collected at numerous springs, they are usually enclosed and connected by pipes to a reservoir or well whence the water flows into the pipes. When water is pumped from a river, the times are chosen when the water is at its best. Conduits, Pipes, etc—The former are preferably used, unle the volume is too small to justify expense, and they are usually open. Tunnels are used when, for any reason, purity may be endangered. Pipes are resorted to for straighter course, or when the level becomes low and pre ure greater, as when a valley is cro ed, or when a break in the grae dient is advisable. See AquepucTs; ATER.