water strider (water strider)

Any aquatic heteropterous insect of the family Hydro head of a suitably situated river by the construction of dams; these are sometimes of great height, holding back bodies of water miles in length. Of this character is the water-supply of Liverpool, of New York, of Boston, and of many other important cities. Regions underlain by thick ma es of permeable rocks-as, for instance, the New Red Sandstone and Chalk districts of England - are not infrequently supplied with water by means of wells bored to considerable depths and of large dimensions, from which the water sometimes rises to the surface, but more often has to be pumped. Many large towns in the manufacturing districts of England were formerly almost exclusively, and are still to some extent, supplied in this way; but wherever it has been found po ible to obtain water in some better way this system has been abandoned, neither quality nor quantity being satisfactory. Considerable water is procured in England from deep wells in the Chalk, and this method of supply is of some importance in London. Where the conditions are such that pure water cannot be had, artificial purification is sometimes resorted to, but this is always expensive and often unsatisfactory. An abundant supply of soft water, taken from some source known to be free from the po ibility of contamination by sewage or otherwise, is one of the greatest of ble ings, and this result has been attained in various cities, but not without large expenditure and no small amount of engineering skill. The distribution of water was once a matter of considerable difficulty, the wooden pipes first employed being subject to rot and leakage. In modern times the use of cast-iron for the mains is most common, while the service-pipes are usually of lead, but sometimes of bronze or bra .