An amazing fact of modern life is that when you turn on a faucet in your home, fresh, clean water comes out. The water comes out due to water pressure. Where does the water pressure come from?
Municipal water systems are pressurized by a combination of gravity, water towers and pumps. Most municipal water systems get their water from surface water such as a lake, river or reservoir. They may also pump water from an aquifer which requires pumps.
After the water is extracted from it’s source, it is treated and purified at a water treatment plant. From there a combination of gravity and pumps deliver water at pressure. For some water systems the source water, whether a reservoir, river or lake, is above the users and gravity alone provides the water pressure.
Water systems also use a combination of pumps and water towers. Water towers use gravity to provide water during high use periods. Typically, water towers are designed to hold an entire day’s worth of water for their service areas. Water from water towers during the day when there is higher demand and are refilled by pumps at night.
Suppose an area has a 500 gallon per minute daily average usage. The minute-to-minute usage will vary widely, with the highest usage typically being in the morning when everyone showers, cooks and brushes teeth, etc. Water towers help meet this demand. Water towers allow the pumps to run at a constant velocity, without having to vary widely to meet varying demand.
Another type of “water tower” used to be used but are actually “standpipes.” Here’s a description from St. Louis City Water:
Before modern pumping methods, the steam-driven pumps that were used to send water throughout the city created large surges in pressure, often causing the pipes to rattle and shake. This also caused multiple-story houses to have difficulty getting water to upper floors. Standpipes (large vertical pipes in which a column of water rose and fell to prevent surges) were built to equalize water pressure. For aesthetic purposes, towers were built to hide the standpipes.
There used to be over 500 of these water tower standpipes all over the U.S. but now due to modern pumping technology they are obsolete. Now there are only seven of them – three of which are in St. Louis. Here are some pictures: