But when ten or a dozen houses began to combine and run their drain-pipes together into a large drain called a sewer, then this could not open upon the surface of the ground, but had to be run into some stream, or brook, in order to be carried away.

As cities and towns, which had been obliged to give up their wells, were beginning to collect the water from these same brooks and streams in reservoirs and deliver it in pipes to all their houses, it can be easily seen that we had simply exchanged one danger for another.
The Loss of Life from Typhoid Fever.

For a time, indeed, it looked as if the new danger were the greater of the two, because, when the typhoid germs were washed into a well, they poisoned or infected only one, or at most two or three, families who used the water from that well.

But when they were carried into a stream which was dammed to form a reservoir to supply a town with water, then the whole population of the town might become infected.

A great many epidemics of typhoid fever occurred in just this way, before people realized how great this danger was.