Water tower

A water tower is an elevated structure that supports a large water tank at a significant height. Its primary purpose is to pressurize a distribution system for potable water, which is water that is safe to drink. These towers also provide essential emergency storage for fire protection. Many water towers work alongside underground or surface service reservoirs. These reservoirs store treated water near the areas where it will be used.

The mechanism of a water tower relies on hydrostatic pressure. This is the pressure produced by the elevation of water due to gravity. As the water sits in the elevated tank, its weight pushes down through the pipes. For every 102mm of elevation, the water produces 1kPa of pressure. A height of 30 meters produces roughly 300 kPa of pressure. This amount is sufficient to meet most domestic and industrial water requirements.

Water towers manage the changing demands of a community through a cycle of storage and refilling. During peak usage hours, such as in the morning or evening, the water level in the tower typically falls. To manage this, pumps refill the tower during the night when demand is low. This cycle also helps prevent water from freezing in cold weather because the water is constantly moving. While the tower provides pressure via gravity, it still requires a pump to refill the tank. Without power, a tower can provide water, but it cannot be refilled for a long time.

The history of water towers traces back to ancient times, but modern pressurized systems developed in the mid-19th century. This growth occurred because steam-pumping became common and better pipes were developed. In the United Kingdom, early systems used tall, N-shaped pipes called standpipes. These standpipes provided pressure relief and helped manage the pulsing flow from steam-driven engines. By the late 19th century, these standpipes were expanded to include storage tanks for growing cities.

Construction materials and shapes for these structures vary widely. Most modern towers are made of steel or reinforced and prestressed concrete. Other materials include wood, fiberglass, or brick. The reservoir itself can be spherical, cylindrical, or an ellipsoid shape. A standard water tower is approximately 30 meters tall. The reservoir inside must have a minimum height of about 6 meters and a minimum diameter of 4 meters.

Specific regional designs offer unique examples of this technology. In New York City, many buildings use small rooftop water towers. The original builders of these New York tanks were actually barrel makers. They used wooden walls held together by steel cables or straps. These wooden tanks do not use a sealant; instead, the wood swells as it becomes saturated to become impermeable. In California, people once built tankhouses to supply individual homes.

Today, water towers often serve purposes beyond simple water storage. Some historic towers have been converted into apartments, penthouses, or even restaurant complexes. Others serve as observation towers or locations for wireless transmission, such as cellular telephone service. In some communities, they become landmarks for local identity. For example, at the University of South Florida, tradition involves lighting the white canvas of the tower in green lights after athletic victories.

Water towers also play a critical role in public health and safety. High volumes and flow rates are necessary when fighting fires, and the tower provides this capacity. If water pressure drops below a certain level, many U.S. states require a "boil-water advisory." This is because low pressure might allow pathogens, or tiny organisms that cause disease, to enter the system. By maintaining steady pressure through elevation, water towers help keep the entire distribution system safe.