The necessity for taking steps to protect the sanitary condition of tidal waters arises chiefly from the plan, now almost universally followed, of employing water to carry off, through sewers, the excrement of the inhabitants of cities.
Originally intended for storm water only, sewers began to be extensively used for the water carriage of excrement about sixty years ago. At that time, and for years afterward, it was not anticipated that the capacity of rivers and harbors for sewage could be exceeded; the only problem seemed to be how to get the offensive material away from the houses and streets of cities and into natural bodies of water with the least inconvenience and expence.
With the progress of time and the growth of cities the amount of sewage disposed of in this manner has enormously increased. Rivers which once furnished wholesome supplies of drinking water and were a source of