Storage, which Sir Alexander Houston has proved with Thames water is capable of rendering a polluted water satisfactory, is unfortunately not practicable in Shanghai, the cost of land and of storage reservoirs of sufficient size to deal with Shanghai's requirements being prohibitive. The removal of suspended impurities is partially accomplished by settle ment, the water to be purified being pumped into tanks, allowed to remain quiescent therein for the necessary period and being then drawn. off and passed to the filters. Alternatively, the water is passed continuously through the settling basins at such velocities as will permit of the desired clarification being obtained. Settlement may be accelerated and the effluent improved by the addition of a coagulant, such as alum, a method which has been used by the Chinese for centuries.
In Shanghai both "intermittent" and "continuous" settling tanks, with and without a coagulant, are
Text read from the printed page and cleaned; old type leaves the occasional error.