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June 2017
3-9
City of Morgan Hill
Water System Master Plan
The minimum acceptable pressure is usually in the range of 40-50 psi, which generally provides
for sufficient pressures for second story fixtures. When backflow preventers are required, they
may reduce the pressures by approximately 5-15 psi. The recommended minimum pressure
during fire flows is 20 psi, as established by the National Fire Protection Association (NFPA).
The City’s pressure criteria are summarized as follows:
Maximum Pressure:
100 psi
Minimum Pressure:
o
Maximum Day Demand: 40 psi
o
Peak Hour Demand, Existing Development: 35 psi
o
Peak Hour Demand, Future Development: 40 psi
o
Maximum Day Demand + Fire Flow: 20 psi
3.5 UNIT FACTORS
Domestic water demand unit factors are coefficients commonly used in planning level analysis to
estimate future average daily demands for areas with predetermined land uses. The unit factors
are multiplied by the number of dwelling units or gross acreages for residential categories, and by
the gross acreages for non-residential categories, to yield the average daily demand projections.
The total domestic water demand was calculated from consumption data. The demand was
adjusted to balance with current production records, and to account for transmission main losses
and vacancies in existing land uses. The demand unit factor was then calculated using the total
water production and total number of residential and non-residential land use acreages.
This analysis generally indicates that existing residential land uses have higher consumptive use
factors than that of non-residential land uses. The existing unit factor analysis is shown on
Table
3.4
. In order to account for continued water conservation efforts implemented by the City, the unit
factors for developing these demands were adjusted to be consistent with projected demands
established in the City’s 2015 UWMP.
3.6 SEASONAL DEMANDS AND PEAKING FACTORS
Domestic water demands within municipal water systems vary with the time of day and month of
the year. It is necessary to quantify this variability in demand so that the water distribution system
can be evaluated and designed to provide reliable water service under these variable demand
conditions.