Water tower
A water tower is an elevated structure supporting a water tank constructed at a height sufficient to pressurize a distribution system for potable water, and to provide emergency storage for fire protection. Water towers often operate in conjunction with underground or surface service reservoirs, which store treated water close to where it will be used. Other types of water towers may only store raw (non-potable) water for fire protection or industrial purposes, and may not necessarily be connected to a public water supply. Water towers are able to supply water even during power outages, because they rely  on hydrostatic pressure produced by elevation of water (due to gravity) to push the water into domestic and industrial water distribution systems; however, they cannot supply the water for a long time without power, because a pump is typically required to refill the tower. A water tower also serves as a reservoir to help with water needs during peak usage times. The water level in the tower typically falls during the peak usage hours of the day, and then a pump fills it back up during the night. This process also keeps the water from freezing in cold weather , since the tower is constantly being drained and refilled. History. Although the use of elevated water storage tanks has existed since ancient times in various forms, the modern use of water towers for pressurized public water systems developed during the mid-19th century, as steam-pumping became more common, and better pipes that could handle higher pressures were developed. In the United Kingdom, standpipes consisted of tall, exposed, N-shaped pipes, used for pressure relief and to provide a fixed elevation for steam-driven pumping engines which tended to produce a pulsing flow, while the pressurized water distribution system required constant  pressure. Standpipes also provided a convenient fixed location to measure flow rates. Designers typically enclosed the riser pipes in decorative masonry or wooden structures. By the late 19th century, standpipes grew to include storage tanks to meet the ever-increasing demands of growing cities. Many early water towers are now considered historically significant and have been included in various heritage listings around the world. Some are converted to apartments or exclusive penthouses. In certain areas, such as New York City in the United States, smaller water towers are constructed for individual buildings. In California and some other states, domestic water  towers enclosed by siding (tankhouses) were once built (1850s–1930s) to supply individual homes; windmills pumped water from hand-dug wells up into the tank in New York. Water towers were used to supply water stops for steam locomotives on railroad lines. Early steam locomotives required water stops every . Design and construction. A variety of materials can be used to construct a typical water tower; steel and reinforced or prestressed concrete are most often used (with wood, fiberglass, or brick also in use), incorporating an interior coating to protect the water from any effects from the lining material. The reservoir in  the tower may be spherical, cylindrical, or an ellipsoid, with a minimum height of approximately and a minimum of in diameter. A standard water tower typically has a height of approximately . Pressurization occurs through the hydrostatic pressure of the elevation of water; for every of elevation, it produces of pressure. of elevation produces roughly , which is enough pressure to operate and provide for most domestic water pressure and distribution system requirements. The height of the tower provides the 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. Using wireless sensor networks to monitor water levels inside the tower allows municipalities to automatically monitor and control pumps without installing and maintaining expensive data cables. Architecture. 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 and motorists. Sometimes the decoration can be humorous. An example of this are water towers built side by side, labeled "HOT" and "COLD". Cities in the United States possessing side-by-side water towers labeled HOT and COLD include Granger, Iowa; Canton, Kansas; Pratt, Kansas, and St. Clair, Missouri; Eveleth, Minnesota at one time had two such towers, but no longer does. 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 facts. A "mushroom" water  tower was built in Örebro, Sweden and holds almost two million gallons of water. Worldwide. The image at the left shows three architectural approaches to incorporating these tanks in the design of a building. From left to right, a fully enclosed and ornately decorated brick structure, a simple unadorned roofless brick structure hiding most of the tank but revealing the top of the tank, and a simple utilitarian structure that makes no effort to hide the tanks or otherwise incorporate them into the design of the building. The technology dates to at least the 19th century, and for a long  time New York City required that all buildings higher than six stories be equipped with a rooftop water tower. Two companies in New York build water towers, both of which are family businesses in operation since the 19th century. 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 are held together with steel cables or straps, but water leaks through the gaps when first filled . As the water saturates the wood, it swells, the gaps close and become impermeable. The rooftop water towers store 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 activate a pump or open a public water line to refill the water tower. Architects and builders have taken varied approaches to incorporating water towers  into the design of their buildings. On many large commercial buildings, water towers are completely hidden behind an extension of the facade of the building. For cosmetic reasons, apartment buildings often enclose their tanks in rooftop structures, either simple unadorned rooftop boxes, or ornately decorated structures intended to enhance the visual appeal of the building. Many buildings, however, leave their water towers in plain view atop utilitarian framework structures. Water towers are common in India, where the electricity supply is erratic in most places. If the pumps fail (such as during a power outage), then water pressure will be lost , causing potential public health concerns. Many U.S. states require a "boil-water advisory" to be issued if water pressure drops below . This advisory presumes that the lower pressure might allow pathogens to enter the system. Some have been converted to serve modern purposes, as for example, the Wieża Ciśnień (Wrocław water tower) in Wrocław, Poland which is today a restaurant complex. Others have been converted to residential use. Historically, railroads that used steam locomotives required a means of replenishing the locomotive's tenders. Water towers were common along the railroad. The tenders were usually replenished by water cranes, which were  fed by a water tower. Some water towers are also used as observation towers, and some restaurants, such as the Goldbergturm in Sindelfingen, Germany, or the second of the three Kuwait Towers, in the State of Kuwait. 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, amateur radio, or cellular telephone service. In hilly regions, local topography can be substituted for structures to elevate the tanks. These tanks are often nothing more than concrete cisterns terraced into the sides of local  hills or mountains, but function identically to the traditional water tower. The tops of these tanks can be landscaped or used as park space, if desired. Spheres and spheroids. The Chicago Bridge and Iron Company has built many of the water spheres and spheroids found in the United States. The website "World's Tallest Water Sphere" describes the distinction between a water sphere and water spheroid thus: The Union Watersphere is a water tower topped with a sphere-shaped water tank in Union, New Jersey, and characterized as the "World's Tallest Water Sphere". A Star Ledger article suggested a  water tower in Erwin, North Carolina completed in early 2012, tall and holding , had become the World's Tallest Water Sphere. However, photographs of the Erwin water tower revealed the new tower to be a water spheroid. The water tower in Braman, Oklahoma, built by the Kaw Nation and completed in 2010, is tall and can hold . Slightly taller than the Union Watersphere, it is also a spheroid. Another tower in Oklahoma, built in 1986 and billed as the ""largest water tower in the country"", is tall, can hold , and is located in Edmond. The "Earthoid", a perfectly spherical tank  located in Germantown, Maryland is tall and holds of water. The name is taken from it being painted to resemble a globe of the world. The golf ball-shaped tank of the water tower at Gonzales, California is supported by three tubular legs and reaches about high. The Watertoren (or Water Towers) in Eindhoven, Netherlands contain three spherical tanks, each in diameter and capable of holding of water, on three spires were completed in 1970. Alternatives. Alternatives to water towers are simple pumps mounted on top of the water pipes to increase the water pressure. This new approach is more  straightforward, but also more subject to potential public health risks; if the pumps fail, then loss of water pressure may result in entry of contaminants into the water system. Most large water utilities do not use this approach, given the potential risks. Examples. Kuwait. Kuwait Towers, which include two water reservoirs, and Kuwait Water Towers (Mushroom towers in Kuwait City. Standpipe. There were originally over 400 standpipe water towers in the United States, but very few remain today, including: