No doubt he makes this statement because he has confidence that the purification of water is both simple and safe. There are two principal methods. The first, and most expensive, is nature's own—the filter. The application of this method is comparatively simple though it involves considerable expense. The trick was learned from the hillside spring which, welling up through strata of sand and gravel, comes out pure and clear and sparkling. To make spring water out of lake water, therefore, it is merely necessary to excavate a considerable area to the desired depth and lead into it the pipes connected with the wells from which water is to be pumped. Then the pit is filled with successive layers of crushed stone graduated in fineness to the size of gravel and then covered with a deep layer of fine sand. This area is then flooded with the water to be filtered, which slowly percolates and comes out clear and pure. The best results in purification of contaminated water supplies have probably been attained in this way; that is, as measured by the improvement of health and the general reduction of the death rate from those diseases caused by the use of contaminated water.
But when the alarm was given this spring by the city chemist there was no time to excavate and build an extensive filtering plant. The dreaded typhoid was already making its appearance and babies were dying. Something had to be done at once.
If some afternoon you take a stroll through Gladwin park your attention may be attracted to a little white building at the lower end of the settling basin. It is merely a temporary structure yet it is serving a very important purpose. Approach the open door and your nostrils will be greeted by a pungent odor that may make you catch your breath. The workmen, too, you will notice, do not stay long within doors, but take refuge in a little shelter booth outside. Strewn about here and there are traces of a white, powdery substance which seems to have been tracked down from a platform erected on the roof. This is hypochlorite of lime, the substance used for sterilizing the city drinking water.
This is so powerful a disinfectant that it destroys all bacteria in water even in an extremely dilute solution. The method of applying it is interesting. The city water comes in from the river through a great tunnel about 10 feet in diameter. The little chlorinating plant is situated on the line of this tunnel so that the solution is readily introduced into the water before it reaches the pool called a settling basin.
The hypochlorite reaches the plant in iron cylinders containing 100 pounds. These are carried up to the roof and poured into the first mixing tank through a hopper fixed for the purpose. There are within the building four of these mixing tanks. In the first, up near the roof, a very strong solution is first made. This is drawn off into a second tank with a greater admixture of water and thence passes into the third and fourth. From the last it is forced out into the main tunnel by a pipe and mingles with the great flood that is pouring constantly into the wells beneath pumping engines. And this is the strength of the chemical: five pounds of it mingled with one million gallons of water is sufficient to render the water fit for drinking purposes. Nearly 98 per cent of the bacteria in the water is destroyed by this weak solution. The water is tasteless and odorless. Indeed, probably very few of the citizens of Detroit who are using the city water all the time, know that the treatment is being applied.
But the chemist continues his tests every morning. Every morning the little crooked tubes are brought out and filled and carefully watched to ascertain if the telltale gas develops which is an index of "death in the cup." Thus is the city's water supply guarded.
No more important work can devolve on the board of health. Before science had learned to recognize the tiny enemies which infest drinking water, typhoid and kindred diseases were regarded as a visitation of divine providence for the sins of a people. We now know that a rise in the death rate from these diseases is to be laid rather to the sins of omission on the part of the board of health and the public works department.
(The Outlook)