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June 2017
3-6
City of Morgan Hill
Water System Master Plan
assumed to have a supply capacity of 800 gallons per minute (gpm). Design criteria for water
supply are documented on
Table 3.3
.
3.3 STORAGE CRITERIA
The intent of domestic water storage is to provide supply for operational equalization, fire
protection, and other emergencies, such as power outages or supply outages. Operational or
equalization storage provides the difference in quantity between the customer’s peak hour
demands and the system’s available reliable supply.
3.3.1
Typical Storage Criteria
Typical storage criteria consist of three main elements: operational, emergency, and fire flow.
Operational Storage
Operational or equalization storage capacity is necessary to reduce the variations imposed on the
supply system by daily demand fluctuations. Peak hour demands may require up to 2 times the
amount of maximum day supply capacity. With storage in place, this increase in demand can be
met by the operational storage rather than by increasing production from the supply sources.
Equalization storage also stabilizes system pressures for enhancing the service. Equalization
storage requirements typically range from 25 percent to 50 percent of maximum day demand. The
City criterion requires that 25 percent of the maximum day demand be reserved for operational
storage.
Emergency Storage
Emergency storage is the volume of water stored to meet demand during emergency situations
such as pipe failures, distribution main failures, pump failures, power outages, natural disasters,
or other cases in which the supply sources are not able to meet the demand condition.
The amount of water reserved for emergencies is determined by policies adopted by the City and
is based on an assessment of the costs and benefits including the desired degree of system
reliability, risk during an emergency situation, economic considerations, and water quality
concerns.
In California, the amount of emergency storage reserve in municipal water systems is usually
between 50 percent and 100 percent of the maximum day demand.
Fire Storage
Fire storage is also needed to maintain acceptable service pressures within a pressure zone, in
the event of a fire flow, which may occur during the maximum day demand. The recommended
fire storage capacity varies by pressure zone and land use type, and is usually higher for