A water tower, watershed, or elevated water tower is a large elevated water storage container. The term tower speaks to its elevation and is constructed for the purpose of holding a supply of water at a height sufficient to pressurize a water supply distribution system. Pressurization occurs through the elevation of water; for every 2.31 feet of elevation 1 PSI (pounds of pressure per square inch) is produced. 100 feet of elevation (@2.34=1PSI) produces 43.3 PSI of pressure, which is enough pressure to operate and provide for most domestic water pressure and distribution system requirements.
Many water towers were constructed during the Industrial Revolution; some are now considered architectural landmarks and monuments, and may not be demolished. Some are converted to apartments or exclusive penthouses.
In certain areas, such as New York City, smaller water towers are constructed for individual buildings.
The users of the water supply (a town, factory, or just a building) need to have water pressure to maintain the safety of the water supply. If a water supply is not pressurized sufficiently, several things can happen:
The height of the tower provides the hydrostatic pressure for the water supply system, and it may be supplemented with a pump. The volume of the reservoir and diameter of the piping provide and sustain flow rate. However, relying on a pump to provide pressure is expensive; to keep up with varying demand, the pump would have to be sized to meet peak demands. During periods of low demand, jockey pumps are used to meet these lower water flow requirements. The water tower reduces the need for electrical consumption of cycling pumps and thus the need for an expensive pump control system, as this system would have to be sized sufficiently to give the same pressure at high flow rates.
Very high volumes and flow rates are needed when fighting fires. With a water tower present, pumps can be sized for average demand, not peak demand; the water tower can provide water pressure during the day and pumps will refill the water tower when demands are lower.
Water towers can be surrounded by ornate coverings including fancy brickwork, a large ivy-covered trellis or they can be simply painted. Some city water towers have the name of the city painted in large letters on the roof, as a navigational aid to aviators. Sometimes the decoration can be humorous, as Granger, Iowa has two water towers, labeled HOT and COLD. The House in the Clouds in Thorpeness was built to resemble a house in order to disguise the eyesore, whilst the lower floors were used for accommodation. When the town was connected to the mains water supply, the water tower was dismantled and converted to additional living space.
Sapp Bros. truck stops use a water tower with a handle and spout – looking like a coffee pot – as the company logo. Many of their facilities have decorated actual water towers (presumably non-functional) on-site.
Many small towns in the United States use their water towers to advertise local tourism, their local high school sports teams, or other locally notable factoids (see images below).
Water towers are very common in India, where the electricity supply is erratic in most places.
In many countries, water towers have been taken out of the water supply system and replaced by pumps alone. Water towers are often regarded to be monuments of civil engineering. Some are rejuvenated and converted to serve modern purposes. For example, the Wieża Ciśnień in Wroclaw, Poland.
Historically, railroads that made use of the steam locomotive required a means of replenishing the locomotive's water reservoirs. Water towers were common along the railroad. Filling these reservoirs was most commonly achieved by means of a water tower feeding one or more water cranes, usually located at stations and locomotive sheds.
Some water towers are also used as observation towers. There are even water towers with restaurants, such as the Goldbergturm in Sindelfingen, Germany. It is also common to use water towers as the location of transmission mechanisms in the UHF range with small power, for instance for closed rural broadcasting service, portable radio, or cellular telephone service.
In the 1800s, New York City required that all buildings higher than six stories be equipped with a rooftop water tower. This was necessary to prevent the need for excessively high pressures at lower elevations, which could burst pipes. In modern times, the towers have become fashionable in some circles. As of 2006, the neighborhood of Tribeca requires water towers on all buildings, whether or not they are being used. Two companies in New York build water towers, both of which are family businesses in operation since the 1800s.
The original water tower builders were barrel makers who expanded their craft to meet a modern need as buildings in the city grew taller in height. Even today, no sealant is used to hold the water in. The wooden walls of the Water Tower walls are held together with cables but leak through every gap when first filled. As the water saturates the wood it swells, the gaps close and become impermeable.
The rooftop water towers store 5,000 to 10,000 gallons of water until it is needed in the building below. The upper portion of water is skimmed off the top for everyday use while the water in the bottom of the tower is held in reserve to fight fire. When the water drops below a certain level, a pressure switch, level switch or float valve will actuate a pump or open a public water line, to refill the water tower.
Famous water towers in the United States include:
Famous water towers in the UK include:
Famous water towers in Slovenia include: