City of Morgan Hill Water System Master Plan 2017

commercial and industrial areas. Fire flow provisions for each pressure zone were calculated based on the governing (highest) land use type within a reservoir service area as follows:

 Residential: 1,500 gpm for 2 hours = 0.18 MG

 Emergency: 2,500 gpm for 2 hours = 0.30 MG

 Industrial: 3,500 gpm for 3 hours = 0.63 MG

Total Storage Requirement

The total storage is the summation of operational (equalization), fire, and emergency storage requirements as follows:

Qs = 25% MDD (equalization) + fire flow (varies) + 25% MDD (emergency)

where:

Qs is the Total Required Storage, in gallons

MDD is the Maximum Day Demand, in gallons

3.4 PRESSURE CRITERIA

Acceptable service pressures within distribution systems vary depending on city criteria and pressure zone topography. It is essential that the water pressure in a consumer’s residence or place of business be maintained within an acceptable range. Low pressures below 30 psi can cause undesirable flow reductions when multiple faucets or water using appliances are used at once. Excessively high pressures can cause faucets to leak and valve seats to wear out prematurely. Additionally, high service pressures can cause unnecessarily high flow rates, which can result in wasted water and high utility bills. The criteria for pressures in the domestic water system include the following:

 Maximum pressure, usually experienced during low demands and winter months

 Minimum pressure, usually experienced during peak hour demands and summer months

 Minimum pressure during fire flows and during the maximum day demand The American Water Works Association Manual on Computer Modeling and Water Distribution System (AWWA M-32) indicates that maximum pressures are usually in the range of 90-110 pounds per square inch (psi). In some communities, the maximum pressure may be limited to 80 psi to mitigate the impact on internal plumbing. In this case, the distribution system is usually sized for the higher pressures, and individual pressure-reducing valves are installed on service lines where the pressure may be exceeded.

June 2017

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City of Morgan Hill Water System Master Plan