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Chapter 4
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Design Criteria
4.18 Water Mains
New water mains are subject to the approval of Seattle Public Utilities (SPU) Project Management and Engineering Division (PMED).
4.18.1 Links to Standard Plans and Specifications

Standard Specification 1-07
Standard Specification 7-10.3(5)C
Standard Specification 7-11
Standard Specification 9-30
Standard Plan 030: Desirable Locations for Utilities (Residential Street)
Standard Plan Section 300: Watermain Appurtenances
Standard Plan 286a and 286b: Sewer and Water Spacing and Clearances
Standard Plan 330a and 330b: Water Main Thrust Blocking Vertical Fittings

4.18.2 Design Criteria

Water main design: SPU PMED provides design criteria for water mains during SIP design guidance

SPU reviews water system designs through the street improvement process.  SPU also reviews proposed work within the right-of-way that may impact existing water mains or water facilities.

Protection of existing facilities: special measures to protect existing or proposed facilities may be required depending on the scope and impact of the proposed water main project. Special protection measures may include the use of restrained joint pipe, corrosion protection, and construction methods that minimize vibration and impacts of excavation to existing utilities.

Pipe material: All materials for water distribution shall be new and conform to Standard Specifications Section 9-30.

Standard location for water mains within the public right-of-way: Water mains will be generally located on the north and east side of the public right-of-way.  In the event that the standard location for water mains is not available the best alignment will be determined during SIP design guidance.

Water valves: Water valves will generally be placed aligned with the perpendicular right-of-way margins, as shown in Figure 4-22: Typical Valve Location. If this location is otherwise unavailable SPU PMED will determine the alternative position. SPU PMED will approve the final location for all water components constructed in the City right-of-way.

Water main, sewer and other utilities separation: Water mains and water service lines shall designed for appropriate separation  from the following:

  • sanitary sewers;
  • storm sewers;
  • combined sewers;
  • house sewer service connections;
  • drains;
  • sanitary sewer force mains; and
  • gas, telecommunications, electrical, and other utilities.

Spacing between water mains and other utilities should comply with City of Seattle Standard Specifications 1-07, and Standard Plans 286a and 286b.

Depth of pipe cover: All pipe shall be laid to a minimum depth as indicated in Standard Specification 7-10.3(5)C and Standard Plan No. 030.

Thrust block: Provide concrete thrust blocks at points where piping changes directions or at dead ends. Thrust blocks shall be designed and installed as indicated in Standard Specification 7-11. Also, thrust blocks must conform to Standard Plan Nos. 330a and 330b.

For pipes larger than 12 inch diameter, or where water pressures are higher and/or soil conditions are poor, the developer engineer shall design the correct block size.  All thrust block designs will require the approval of SPU PMED prior to installation. The stamped calculations shall be submitted to SPU PMED for review and approval.

Test pressure for field testing water main pipe: Field pressure testing for water mains shall be in accordance with Standard Specification 7-11. 3(1).  Field hydrostatic testing of various diameter ductile iron water main pipes and appurtenances shall be:

Test Pressure for Field Testing Water Main Pipes

Diameter Pipe (inches) 4 6 8 10 12 16 or larger
Test Pressure (psi) 300 300 300 300 300 250

Flushing and disinfection: Before being placed in service all newly installed pipes, valves, hydrants and appurtenances shall be flushed, disinfected and kept clean, and an acceptable bacteriological report shall be obtained. Flushing and purification shall be in accordance with Standard Specification 7-11.

Vault location: Prior to water service approval, SPU Customer Service shall coordinate all work associated with installation of service vaults. The table below provides some preliminary information. SPU Water Crews will perform all service work.

Water services: For further inquiries regarding water services please contact SPU Customer Service or refer to:

Vault Location by Meter Size and Type

Vault Meter Size and Type General Location in the ROW
3/4" & 1" Domestic See City of Seattle Std. Plan #286b
1 1/2" & 2" Domestic See City of Seattle Std. Plan #286b
3" & 4" Domestic

Vault plan required. Installation by SPU Crews),contact SPU Customer Service

6" Domestic
2" DC Fire Service

Direct-bury in approved enclosure (meter box), standard pending.  Installation by SPU Crews, contact SPU Customer Service

4"-10" x 3/4" DC Fire Service
4" Combination Service Vault plan required. Installation by SPU Crews, contact SPU Customer Service
6" Combination Service
8" Combination Service


4.18.3 Design Considerations
  • Consider how to maintain fire flow during construction activities.
  • Coordination with SPU water operations is required for all new connections, services, meter installations and any temporary cut and caps or temporary mains to facilitate your construction.
  • Provide notice to the Fire Department if flow will be impeded and what provisions have been made – also note if access at the site will be limited or if street access will be limited.
  • Be sure to check for utilities in the project alignment especially around large service locations as they could interfere with water mains, blocking, or meter vault installations.
  • Only SPU crews are allowed to operate the existing water system for public health and safety reasons. Plan to coordinate with SPU water crews well in advance of starting construction to have your work added to crew work schedules.
continue to section 4.19»   
Latest Online Manual
Detailed Table of Contents
Chapter 4
Design Criteria
4.1 Introduction
4.2 Street Classifications and Street Types
4.3 Design Criteria General Notes
4.4 Grading
4.5 Design Cross Section
4.6 Roadway Width

Roadway Pavement

4.8 Intersections
4.9 Driveways
4.10 Curbs
4.11 Sidewalks
4.12 Crosswalks
4.13 Bicycle Facilities
4.14 Street Trees and Landscape Architectural Standards
4.15 Introduction to Utilities Design Criteria
4.16 Street Lighting
4.17 Street Drainage, Storm Drains and Sewers
4.18 Water Mains
4.19 Fire Protection
4.20 Seattle City Light
4.21 Clearances
4.22 Structures in the Right-of-Way
4.23 Culdesacs and Turnarounds
4.24 Traffic Operations
4.25 Transit Zones
4.26 Street Furniture, Public Art and Unique Objects in the Public Right-of-Way
4.27 Access Easements
4.28 Contact Information
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