Service storage / Distribution storage
Distribution storage or storage within the distribution system allows constant rate of distribution in case of unusual demand.
The principal functions of distribution storage are:
- to equalize supply and demand
- to provide water for fire fighting
- for emergency purposes
Distribution storage consists of the following components.
- equalizing or operating storage
- fire storage or reservoir
- emergency reserve
Equalizing or operating storage
It equalizes supply and demand which depends on variation in demand and supply hours.
Equalizing storage permits the supply, treatment, pumping and transfer works at a capacity equal to the average rate during maximum day. If demand is above than the average, then it is supplied through storage. There are significant variations in water demand at different time period of the day.
Adding supply, treatment and pumping capacity to the system to meet the demand above the average rate on maximum day, and thereby avoid the need for equalizing storage, is far more costly than providing equalizing storage for this purpose.
Its function is to meet the fire demand.
Its function is to meet the demand in case of system failure. Emergency storage is used to meet the demand in case of any disturbance in supply. Disturbance may be source contamination, equipment failure, pipeline breaks or power failure. It can also be used for large fires which consumes the design fire reserve volume. Generally emergency storage is not more than 25 % of the total storage.
Location of storage facilities can greatly affect overall system cost and performance. Following considerations must kept in mind for effective placement of future storage:
- The location and capacities of supply, pumping, transmission and storage facilities.
- The condition of existing storage facilities.
- The compatibility of existing storage facilities with future requirements.
- The size, shape and topography of the water districts.
- The relative economics of constructing additional pumping and transmission facilities versus additional storage facilities.