Guarding a City’s Water Supply
How the City Chemist Watches for the Appearance of Deadly Bacilli; Water Made Pure by Chemicals
“COLON.” The city chemist spoke the one significant word as he set down the test tube into which he had been gazing intently. The next morning the front page of all the city papers displayed the warning, “Citizens should boil the drinking water.”
Every morning, as the first task of the day, the city chemist uncorks a curious little crooked tube containing a few spoonsful of very ordinary bouillon, akin to that which you might grab at the quick lunch, but which has been treated by the admixture of a chemical. This tube begins in a bulb which holds the fluid and terminates in an upturned crook sealed at the end. Into this interesting little piece of apparatus, the chemist pours a small quantity of the city drinking water, and he then puts the whole into an incubator where it is kept at a temperature favorable to the reactions which are expected if the water is contaminated.
After a sufficient time the tube is inspected. To the untrained eye nothing appears. The bouillon still remains in the little bulb apparently unchanged. Its color and clearness have not been affected. But the chemist notices that it does not stand so high in the closed end of the tube as it did when placed in the incubator. The observation seems trivial, but to the man of science it is significant.
What has happened? The water contained some minute organisms which when acted upon by the chemical in the tube have set up a fermentation. Gradually, one by one in the little bulb, bubbles of gas have formed and risen to the surface of the liquid in the closed upper end of the tube. As this gas was liberated, it took the place of the liquid in the tube, and the liquid was forced downward until there was quite a large space, apparently vacant but really filled with gas.
It was this phenomenon that had attracted the attention of the chemist. What did it mean? It was the evidence that the water which was being furnished to the city for half a million people to drink contained some living organism.
Now that, in itself, was enough to make an official of the health department begin to take an interest. It was not, however, in itself a danger signal.
Not all bacterial life is a menace to health, the chemist will tell you. Indeed, humanity has come to live on very peaceable terms with several thousand varieties of bacteria and to be really at enmity with but a score or more. Without the beneficent work of a certain class of bacteria the world would not be habitable. This comes about through a very interesting, though rather repulsive condition—the necessity of getting rid of the dead to make room for the living.
What would be the result if no provision had been made for the disintegration of the bodies of all the men and animals that have inhabited the earth since the beginning? Such a situation is inconceivable. But very wisely providence has provided that myriads and myriads of tiny creatures are ever at work breaking up worn-out and dead animal matter and reducing it to its original elements. These elements are taken up by plant life, elaborated into living vegetable growth and made fit again for the nourishment of animal life, thus completing the marvelous cycle. And so we must not get the notion that all bacteria are our mortal foes. We could not live without them, and our earth, without their humble services, would no longer be habitable.
Neither need we fear the presence of bacterial life in our drinking water. Drinking water always contains bacteria. We, ourselves, even when in the best of health, are the hosts of millions upon millions of them, and it is fair to suppose that they serve some useful purpose. At any rate, it has never been demonstrated that they do us any harm under normal conditions.
And so, the chemist was not alarmed when he discovered that the formation of gas in his crooked tube gave indication of bacteria in the drinking water. He must ascertain what type of bacteria he had entrapped. To this end, he analyzed the gas, and when he determined that the fermentation was due to the presence of colon bacilli in the water, he sent out his warning. Not that the colon bacilli are a menace to health. The body of every human being in the world is infested with millions of them. But the presence of colon bacilli in drinking water is an indication of the presence of a really dangerous thing—sewage.
Thus, when the city chemist turned from his test tube with the exclamation, “Colon!” he did not fear the thing that he saw, but the thing that he knew might accompany it.
There has been much discussion of late of the possibility that the great lakes cities may suffer a water famine. The rapid increase of population along the borders of these great seas, it has been said, might render the water unfit for use. This fear is based upon the assumption that we shall always continue the present very foolish practice of dumping our sewage into the source of our water supply. The time may come when we shall know better how to protect the public health and at the same time husband the public resources. But even at that, the city chemist says that he hardly expects to see the time when the present intake for water near the head of Belle Isle will not be both safe and adequate.
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)