Why Water does not always flow from a Faucet

The Water Problem of a Large City:
Most of us have at times been annoyed by the inability to secure water on an upper story, because of the drawing off of a supply on a lower floor. During the working hours of the day, immense quantities of water are drawn off from innumerable faucets, and hence the quantity in the pipes decreases considerably unless the supply station is able to drive water through the vast network of pipes as fast as it is drawn off. Buildings at a distance from the reservoir suffer under such circumstances, because while the diminished pressure is ordinarily powerful enough to supply the lower floors, it is frequently too weak to force a continuous stream to high levels. At night, however, and out of working hours, few faucets are open, less water is drawn off at any one time, and the intricate pipes are constantly full of water under high pressure. At such times, a good flow is obtainable even on the uppermost floors.

In order to overcome the disadvantage of a decrease in flow during the day, standpipes are sometimes placed in various sections. These are practically small steel reservoirs full of water and connecting with the city pipes. During "rush" hours, water passes from these into the communicating pipes and increases the available supply, while during the night, when the faucets are turned off, water accumulates in the standpipe against the next emergency (Figs. 151 and 154). The service rendered by the standpipe is similar to that of the air cushion.

FIG. - A standpipe.