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Planning guideWater extraction and supplyWater storage tanksThe water must be placed in intermediate storage after it has beentreated for the respective application. Storage facilities for potablewater or process water are referred to as water storage tanks or waterreservoirs.Types of reservoirsA distinction is made between natural and artificial reservoirs. Naturalreservoirs are, for example, oceans and seas, lakes and rivers aboveground or ground water. Artificial reservoirs are, for example, undergroundtanks or reservoirs formed by dams.Underground tanksThe water level of the storage tank is lower than that correspondingto the supply pressure. The water must therefore be pumped up outof the tank for supply purposes. Underground tanks are thereforesuction tanks for pumping station units and are used for compensationbetween spring water inflow or preliminary well pumping andraising the water into the supply system. With pressure vessel pumpingstations, they also assume some of the tasks of elevated tanks,such as the compensation of consumption fluctuations or the storageof fire-fighting water.Water towerWater towers can store only small amounts of water, but neverthelessprovide sufficient pressure for the pipe systems below them dueto their static head.If no favourably positioned ground site is available, then water storageis carried out in the vicinity of the supply area in water chamberswhich are located, in the upper part of a tower-like building structure.The water tower is occasionally designed as a standpipe tower,where the bottom of the water chamber is the foundation bed. Thecosts of a water tower are considerably higher than those of aground-level container (around 5 to 10 times as high). The water levelof the storage tank is therefore generally not positioned as highabove the supply area as is the case with a ground-level tank, and itsvolumetric capacity is kept smaller.Fire water tankVery frequent, and in the case of small rural communities almost alwaysnecessary, is the storage of fire water in special fire water tanks,e.g. when no central water supply is available or when the water supplyin the elevated tank is not sufficient for fighting major fires. Surfacewater can also be used for filling purposes, since the water is notsubject to any special hygienic or technical requirements. Generally,nearby ponds are equipped with the equipment required for extractingfire water or artificial fire protection ponds (fire ponds) are created.Underground fire water tanks are on the other hand more practicalin closed areas covered with buildings.Elevated tankThe most common form of water storage and the one to be used inmost central water supply systems is in elevated tanks. These are waterstorage tanks in which the water level is higher than the supplyarea from which the water falls along a natural gradient to flow intothe supply system. They are used for compensating consumptionfluctuations, for maintaining a consistent pressure in the supply system,for emergency supplies and for the storage of a water reservefor fire-fighting purposes, with long-distance lines and with groupwater supply systems such as interim tanks and zone tanks.If the elevated tank is set up at an appropriate height, then it alsoprovides the required supply pressure. It is possible to have elevatedtanks arranged at different static heads in order to provide differentpressure stages (hilly countryside). Tanks are, however, used not onlyfor water storage but also for pressure reduction; it is primarily insupply networks with large static head differentials that so-calleddischarge flow-through tanks are used, since otherwise the pressureat the lowest point of the water supply system would be too great.Ground-level tankThe water storage tank is set up at a favourable location in terms ofaltitude and position, with most of the structure installed undergroundand covered with earth. This form of elevated tank is frequentlypreferred, because it is the most economic and reliable typeavailable.10 Wilo Water Management catalogue – 50 Hz – Water supply – Raw water intake – Edition 2012/2013 – Subject to change without prior notice