Perhaps the most important sanitary question now pressing for solution is that of a pure water supply for our towns and cities. As this country becomes more populous, the streams and lakes receive more refuse and sewage, until the purification of the water supply for a given locality has become the crying need. Statistics show that at least 55 per cent, of the waters supplied to cities and towns are obtained from surface sources and are necessarily liable to more or less contamination. Various remedies have been sought for this condition, the most practical thus far suggested is to prevent the contamination, by carefully guarding the lakes or rivers from which the supply is obtained. It is at once apparent that only a certain degree of security is reached in this way, as it is clearly impossible to perfectly guard an extended water shed.
Aside from organic or infectious pollution,