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City of Milpitas
Engineering Design Guidelines
Water (Potable)

The information and guidelines contained herein are to be used whenever applicable. In the event a development is to be constructed in stages, master utility plans are required prior to submittal of the first stage improvement plans. The master utility plans shall show all improvements, including interim (phased) and ultimate improvements. For information regarding these guidelines contact the Land Development Section of the Engineering Division, at (408) 586-3329.

The City potable water distribution supply consists of two water systems separated from each other – the San Francisco Public Utilities Commission (SFPUC) and Santa Clara Valley Water District (SCVWD) systems. Each system is divided into pressure zones with greater hydraulic gradients provided in the higher elevations to the east. Care shall be provided to avoid mixing water supply and/or pressure zones. See Exhibit A for Water Supply and Distribution Map to determine water pressure zones.

Submittals shall show water pipes, appurtenances including valves (isolation, air relief, blow-off, etc.), laterals, fire hydrants and size and location of water meters, backflow devices, and intended use of water (potable irrigation).

Note:

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Design Criteria

  1. Fire Flow

    Residential areas – provide 1500 gallons per minute (gpm) minimum fire flow, simultaneous with the maximum day demand of the area.

    Multiple family areas – provide 2500 gpm minimum fire flow, simultaneous with the maximum day demand for the area.

    Commercial areas - provide 3000 gpm minimum fire flow, simultaneous with the maximum day demand for the area.

    Industrial areas - provide 5000 gpm minimum fire flow, simultaneous with the maximum day demand for the area.

    If two or more uses are combined, the higher value use should govern.

  2. Backbone Water Distribution System

    Special design of pipelines along the City’s backbone distribution alignments shall apply. The purpose of a backbone line is to withstand a design earthquake.  Exhibit B-1 shows the alignment where special design standards apply. Exhibit B-2 shows the design standards that apply.

  3. Material
    1. Polyvinyl Chloride (PVC) Pipe  PVC pipe shall conform to the requirements of “Standard Specifications for PVC Pipe” (AWWA C900), or (AWWA C905). However, C905 pipe may be allowed in areas where there is no requirement for future tapping of the transmission line upon approval.
    2. Ductile Iron (DI) Pipe  DI pipe shall conform to the requirements of “Standard Specifications for DI Pipe” ANSI A21.51 (AWWA C151).

  4. Headloss

    Design velocity shall not exceed 8 feet per second. Headloss for pipes less than 16 inches diameter shall not be greater than 10 ft/1000 ft (4.2 psig per 1000 feet). Headloss for pipes equal to or greater than 16 inches diameter shall not be greater than 5 ft/1000 ft (2.2 psig per 1000 feet).

  5. Minimum Pressure

    Residual pressure under fire flow conditions shall be 20 psi or greater. Call the Utility Engineering Section at 586- 3350 or 586- 3348 for water pressure information at specific locations.

  6. Friction Factor

    The Hazen & Williams formula with the coefficient of friction "c" = 110 for all pipe shall be used.

  7. Water Demands

    Design shall include unaccounted water loss adjustment when sizing distribution pipes; unaccounted for water losses shall be assumed to be at least 7% of calculated total demand.

    The following flow factors are criteria for minimum required capacity. Professional engineering judgments shall be used for small and some individual developments since the capacity determined by calculations may be inadequate.

    Commercial: Town Center Area 10,900 GPD/Net Acre*
      Mixed Use 10,900 GPD/Net Acre
      Retail Sub-center (RSC)         4,300 GPD/Net Acre
      Professional/Admin Offices (PAO) 3,200 GPD/Net Acre
      Other 2,400 GPD/Net Acre
    Industrial:   Manufacturing/Warehousing 2,000 GPD/Net Acre
      Industrial Park 1,250 GPD/Net Acre
    Residential: Residential** 320 GPD/DU
      Residential*** 245 GPD/DU
      Residential**** 800 GPD/DU

    *
    GPD is gallons per day. Net area is defined as development area excluding major public streets, freeways and railroad areas.
    **
    DU is dwelling unit. Valley floor low and medium single family.
    ***
    Valley floor multiple family medium, high and very high.
    ****
    Hillside homes (areas above 200 feet elevation).

  8. Peaking Factors
     
    Maximum Day/Average Dav
    Peak Hour/Average Hour
    Residential
    190%
    380%
    Commercial/Industrial
    150%
    240%

  9. Easements

    10 feet wide (minimum). Trees and deep-rooted plants are not permitted within easements.

  10. Pipeline Locations

    5 feet to the pipe centerline from face of curb, on the opposite side of the storm drainage line. Also, see Exhibit C for October 16, 2003 California Department of Health Services guidance criteria for minimum separation distance between sewer, storm, and recycled water lines.

  11. Distribution System Valves
    1. Valves shall be gate valves (AWWA).
    2. Maximum 500 feet apart (may vary for transmission main).
    3. Provide at least one isolation valve between any two fire hydrants.
    4. One at each leg of crossings.
    5. The valve covers shall be as follows:
      9 inch circular black to designate SFPUC
      6 inch circular blue to designate SCVWD
      12 inch circular red to designate ISOLATION between SFPUC and SCVWD

  12. Pipe Cover (minimum)
     
    1. Streets - 42 inches
    2. Easement - 48 inches

  13. Pipe Size (minimum)
     
    1. Residential = 6 inches (8 inches if flow is provided from one direction)
    2. Industrial/Commercial = 12 inches

  14. Air Relief and Blow-off Valves

    Provide appropriate air relief valves (pressure air release at all high points to vent; air and vacuum to vent air while filling and to allow air to re-enter while draining to prevent collapse, etc.) at all high points. Air relief valve and air vacuum valve shall be located above ground. Also provide blow off pipe and valve at all low points.

  15. Pipe Crossing Clearance

    Minimum pipe crossing between pipes clearance shall be not less than one foot. Potable water lines shall be located above storm drain, sanitary sewer and recycled water lines. See Exhibit C for DOHS October 16, 2003 guidelines.

  16. Dead Ends

    End lines with a blow off valve, air and vacuum valve and plugged end assembly.

  17. House Laterals

    Use Copper for all house services (2 inch or smaller) from water main to water meter.

  18. Fire Hydrants
    1. Type shall be as specified in Standard Drawing No. 742 or approved equal list. In general, a two-port hydrant is used in single-family residential areas and a three-port hydrant is used in all commercial, industrial and multiple family areas.
    2. Spacing - maximum 500 feet apart in single family areas and 300 feet apart in all other areas.
    3. Cul-de-sac street - locate hydrant a minimum of 100 feet and a maximum of 200 feet from the end of the street. If the hydrant is 300 feet or less from the connecting street, a 6" line may be used. If greater than 300 feet, use an 8" line, or looped 6" line. No fire hydrant shall be allowed on a 6" line farther than 600 feet from its connection to a larger line, even in the case of a looped line.
    4. Service lateral connections are not allowed on pubic fire hydrant laterals.

  19. Water Service Agreement Required

    Developer shall complete Water Service Agreement to obtain water service (contact Land Development Engineering). Water service shall be issued prior to building permit issuance.  All water services and meters shall be sized by the Developer’s Engineer per AWWA M6 Manual and reviewed by the City.

    Residential development: minimum service/meter size may be required by City on a case-by-case basis. Hillside residences with fire sprinkler systems shall have a minimum of l" water service and l" water meter. Non-single family swimming pools (e.g. clubhouses) shall be served by a separate domestic water meter and backflow device; Wet tap of the same size or larger than the water main is not allowed.  Separate irrigation meters and backflow devices are required for all uses except common areas within single family lots.

    Commercial development: separate domestic meters are required for each building and are highly recommended for each tenant space (provides advantage to tenant and owner since most appropriate sewer service charge can be applied). Split service from the detector check lateral is not allowed for services less than 8”, or if the domestic or irrigation split service is greater than 2”.

  20. Backflow Preventers

    Backflow preventers after the water meter shall be installed for all new developments (see City Standard Drawing No. 734).  A reduced pressure principal (RP) backflow prevention device shall be installed on all irrigation systems. An RP backflow prevention device shall be installed on all domestic systems, except residential services serving two or less dwelling units. No backflow device is required on residential services serving two or less dwelling units, unless potential for contamination of the public water system supply exist (see Ord. 233, Section VIII). A reduced pressure principle detector check (RPDA) assembly shall be installed on all fire services which may have direct connection with pumps, injectors, pressurized tanks, auxiliary water supplies, or elevated storage tanks (Class III, IV, V and VI).  On sites where both potable and recycled water supply exists, a reduced pressure principal backflow preventor (RP) shall be installed on the potable supply line. A double check detector assembly (DCDA) shall be installed at public water line connections for all looped private fire service lines.  An RPDA assembly may replace DCDA on a fire service requiring an DCDA assembly. All backflow prevention devices shall be installed per City Standard Drawing No. 734 and shall be tested upon installation and annually thereafter.  All testing results shall be submitted to the Utility Section of the Engineering Division.

  21. Sampling Stations

    Water quality sampling stations on the distribution line may be required. See standard details.

  22. Corrosion Control

    All metallic piping shall be protected against corrosion per City standard specifications. Include the City’s standard cathodic test station data table.

See Improvments Plans General Requirements for more information.