Water storage is essential for meeting all of the domestic, industrial and fire demands of most public water systems. The type and capacity of water storage required in a distribution system vary with the size of the system, topography of the area, how the water system is laid out and various other considerations. The four types of water storage structures, depending on the need of that specific community, are hydro pneumatic tanks, ground-level reservoirs, buried reservoirs and most commonly, elevated tanks.
Water storage tanks can be used for either operating storage or emergency storage. An operating storage tank generally “floats” on the system. In other words, the tank is directly connected to distribution piping, and the elevation of the water in the tank is determined by the pressure in the system. Water flows into the tank when water demand is low, and it empties from the tank when demand exceeds supply.
Emergency storage is designed to be used only in exceptional situations, such as high-demand fires. A tank installed by an industry for use with the industry’s own fire protection sprinkler system is an example of emergency storage. Due to emergency storage water not being turned over, it stagnates, loses all residual chlorine and can become contaminated. It cannot be used as potable water unless it is treated further. If the emergency water storage tank is located in a cold region, it must be circulated and heated to prevent the water from freezing in the winter months.
Distribution storage facilities can either be located at the ground level or elevated. Elevated tanks generally consist of a water tank supported by a steel or concrete tower. In general, this is the type of tank that floats on the distribution system. Occasionally, system pressure could become so high that the tank would overflow. Commonly in these cases, an altitude valve must be installed to prevent the tank from overflowing.
Reservoirs have a very wide range of meanings in the water supply field. For raw water, reservoirs are generally ponds, lakes or basins that are naturally formed or constructed for water storage. For storage of finished water, the term is usually applied to large aboveground or underground storage facilities. Distribution system reservoirs are usually used where very large quantities of water must be stored or when an elevated tank is objectionable to the community. Commonly elevated tanks will be constructed on a high-rise ground, so it can float the system. The reason for this is that water can be directly available to the system without the need of pumping.
Depending on the area of the country where you reside, the type of water storage that is used depends on the demand and geography. System requirements can vary, as well. For more information about storage tanks, please visit http://www.awwa.org.