Other Answers (1)

• 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 low demands jockey pumps are used to meet these lower water flow rate requirements. The feed from these pumps and a water tower first go to a Hydropneumatic Pressure Vessel. This Pressure Vessel is an Air over Water Device, used to produce a consistent pressure with either a force (PSI) generated by pump or the water tower%26#039;s hydrostatic force in combination with a trapped volume of air; this is where the water meets the citizens%26#039; demand for a constantly varying output pressure wate supply. 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.
  
  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:
  
  Water may not reach the upper floors of a building;
  Water may not spray from a tap with sufficient flow
  Without a water tower, parts of gravity flow water supply systems in hilly areas may be subject to negative pressures (see siphon). Negative pressure in the system may cause shallow groundwater to be sucked into a leaky water supply system, polluting it with microorganisms, dirt, sand, fertilizers, and any other toxic contaminants that may be in the groundwater;
  Water towers are able to supply water even during power outages, because they rely on pressure produced by elevation of water (due to gravity) to push the water pipes into domestic and industrial water distribution systems; however, they cannot supply water for a long time without electricity because a pump is required to refill the tower.
  A further purpose is that a water tower 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.
  
  If you need anymore information just go to the source. It has everything there http://en.wikipedia.org/wiki/Water_tower