Water Distribution System Design

A water system must safely convey the required amount of high quality water throughout a sound distribution system at the least cost. Therefore, the Engineer must consult pertinent and current requirements from federal, State, and regional agencies to ensure the system complies with all standards and regulations.

Drinking Water System Regulators
*Environmental Protection Agency (EPA)
*California Department of Public Health
*California Public Utilities Commission
*County/City Department of Public of Works
*California Administrative Code, regarding cross-connections and backflow prevention.
*Uniform Fire Code

Improvement Plans Requirements
Provide a detailed utility plan showing onsite and offsite public and private water and fire protection systems, including appurtenances and connections. Show location, pipe material, diameters, fire hydrants, valves, backflow protection, horizontal and vertical separations, slopes, cover, inverts, laterals, right-of-way, crossings, and any other necessary facility to demonstrate compliance with engineering principles and agencies regulators.

Materials
Public water mains may be constructed of PVC (http://www.plasticpipe.org/), Ductile Iron (http://www.dipra.org/), ReinforcedConcrete Pipe, RCP (http://www.concrete-pipe.org/), or Wrapped Steel Pipe. Asbestos cement pipe are not allowed under any circumstances.
*Mains eight (8) to twelve (12) inches in diameter will be PVC, pressure class 150, DR 18, AWWA Standard C900 or Ductile Iron, pressure class 350 per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, DI or PVC Pressure Class 200, DR14 must be used.
*Mains sixteen (16) inches in diameter will be PVC, pressure rating 165psi, AWWA C905, DR25 or Ductile Iron (DI) per AWWA Standard C151. Where the normal mainline static pressure exceeds 100 psi, AWWA Standard C905, DR18 with a pressure rating of 235 psi or Ductile Iron (DI) Pipe must be used.
*Mains twenty (20) inches in diameter and larger water mains will be concrete cylinder pipe, wrapped steel pipe, or Ductile Iron.
*Service laterals will be copper, PVC, or DIP per applicable City Standards.

Alignment
Public water mains shall be designed inside the street right-of-way. In general, public water systems shall be designed only where they serve multiple lots and where appropriate access for maintenance can be provided.
Horizontal Alignment
*Conform to the State of California Department of Health Services “Criteria for the separation water Main and Sanitary sewers”, appendix A. In general, ten (10) feet wall to wall separation.
*Conform to manufacturer requirements for minimum allowable radius curvatures. In situations such as streets with smaller radius curves, the water system will be designed in straight segments parallel to the sewer or storm drain system.
*Minimum separation from storm drains is five (5) feet and from monuments, gas, electrical, phone, cable and other dry utility shall be four (4) feet clear.
*All public water mains must be designed a minimum of five (5) feet from all structures such as manholes or drop inlets. A minimum of three (3) feet from the lip of gutter shall be provided.
* Five (5) feet separation from the edge of easements shall be provided for public water mains.
*Dual water mains shall have a minimum five (5) feet clear horizontal separation.
*Crossings shall be designed close as 90 degrees to that facility. Crossing less than 45 degrees will only be approved when no other design is possible.
*Minimum separation between water and sewer lateral services shall be five (5) feet clearance.
Vertical Alignment
*Provide a minimum of six (6”) inches of vertical separation from storm drains and “dry” utilities.
*Conform to State of California Department of Health Services “Criteria for the Separation of Water Main and Sanitary Sewers”, Appendix “A”. In general, one (1) foot wall to wall separation.
*When the minimum cannot be maintained, concrete encasement or ductile iron pipe may be submitted for approval.

Main Sizing Criteria
*Allowable nominal sizes for public water mains are 8”, 12”, and 16”. The minimum new public main size for residential developments is 8" inches and when serving industrial/commercial and/or multi-family residential developments greater than two units, must be a minimum of 12" inches.
*Public water mains must be sized to meet minimum Fire Code requirement in addition to domestic and irrigation demands.

Cover
*Cover is the distance from the top of the pipe to final finished grade. Typically the minimum standard depths of cover for 4” to 8” inches water mains is 3”-0” feet; for mains 10” to 12” shall be 3’-6”; and for mains 16” or greater minimum cover is 4’-0”.
*Where standard cover cannot be maintained, either an under-crossing or over-crossing shall be provided.

Design Criteria
*Operation Conditions
Pressure (psi) and velocity (fps)
Maximum day: 60 psi(max); 40 psi (min); 5 fps (max)
Maximum day and Fire: 80 psi(max); 20 psi(min); 10 fps (max)
Peak hour: 80 psi(max); 30 psi(min); 7 fps (max)
*If pressure measured at any faucet is less than 35 psi, a pressure booster system is required. If pressure at any faucet exceeds 80 psi, a private pressure regulating device is required.

Rate of Domestic use
*Land Use
Average Day Demand (ADD) - Gallons per Acre Day
Fire Flow (FF) - Gallons per minute (gpm)
Fire Duration (FD) - Hour (hr)
Low Density Residential: 2,500(ADD); 1,500(FF); 2(FD)
Medium Density Residential: 3,200(ADD); 1,500(FF); 2(FD)
High Density Residential: 3,600(ADD); 2,500(FF); 3(FD)
Commercial: 2,200(ADD); 3,000(FF); 3(FD)
Schools: 2,200(ADD); 4,000(FF); 4(FD)
*Potable water demand for planning purposes shall be estimated using the water demand factors outlined in the Master Plan.
**Maximum Day Demand (MDD) = 2.0xAverage Day (ADD)
**Peak Hour Demand = 4.0xAverage Day (ADD)
** The Hazen-William formula shall be used in the hydraulic study of the system, using a “C” value of 130 for cement-lined pipe, PVC C900, and ductile iron pipe.

Looping
For system reliability, to minimize pipe size, and to minimize the number of people affected by a system shutdown, either for domestic or fire protection purposes, no more than 100 residential units may be served by a single-feed water system. Where more than 100 units are to be served, a dual-feed (or looping) public water system must be designed.

Valve Placement
*Intersecting mainlines should be equipped with isolation or shut-off valves (usually gate valves) to minimize disruption during repairs. “T” intersections typically require three valves and cross intersection typical require four valves.
*Valves within 250' feet of an intersection may be considered as part of the intersection.
*All hydrants must be on separately valved sections of the public main.
*Valves shall be designed to maximum interval of 1,000 feet.
Air release and Vacuum relief valves (ARV)
*Air release and vacuum relief valves are required at substantial high points in the system that are one pipe diameter or higher than the remainder system, such as over a hilltop or at the upper end of a dead end main.
Pressure reducing valves (PRV)
*Design pressure reducing valves to maintain overall system balance and to maintain service pressure levels within the parameters established within the system design standards.
Backflow Prevention Devices
These devices are a reasonable and effective mean of protecting water system from backflow.
Backflow prevention devices or air-gaps of a type shall be located as close as possible to the service connection and shall be installed as follow:
*Premises within which any substance is handled under pressure that could potentially permit backflow or back-siphonage into the potable water system.
*Premises which have more than one service connection and which may contain cross-connections that may result in the pollution of the potable water system.
*Premises having gray and/or recycled water use systems.
*Examples of premises which require the installation of a backflow prevention device are: Auto repair/painting, car wash, chemical or processing facilities, fire systems, gas stations, hospital and medical facilities, irrigation systems, restaurants, schools, laundry facility, swimming pool.
**All backflow devices must be listed on the latest revision of the approved USC Foundation for Cross-Connection Connection and Hydraulic Research list. List includes (manufacturer’s name, model, size, etc).
**In General City standards provide a list of premises requiring backflow prevention devices along with the type needing to be installed (Air gap, double check, reduced pressure, double check with detector).

Fire Hydrants
*Design of hydrant locations must meet the Fire Code requirements and be approved by the Fire Department for logistics and by the Utilities Department for maintainability. In general, hydrants shall have 500’ feet maximum spacing or 300’ feet in high fire severity zones.
*Locate hydrants at intersections. If not possible locate them near a property line, and/or five (5’) feet from residential driveways.

Joint Restraint
Thrust blocking or restraints should be provided where changes in water direction occur and where reductions in pipe diameter are made and dead ends. A concrete mass or a mechanical joint restraint device may provide thrust restraints. Water mains installed at a slope of fifteen (15) percent or greater will be designed with restrained joints.
*Typical standard bend angles (degrees) are: 11 ¼ , 22 ½, 45, 90.

Hot Tap
Hot taps are not allowed within two (2’) feet of a joint, otherwise, a “cut-in-tee” shall be used.

Easements
An easement must be provided over any public water system when it is outside the public right-of-way. The easement must be a minimum of fifteen (15’) feet wide if it only contains a water main or twenty (20’) feet if it contains another facility. Separate access easements may be required depending on site conditions.
No structures may encroach on, above or below the surface of the ground in any public water easement.

Abandonment of water mains and services
*remove the valve and saddle for all water services two (2) inches or less and install a full circle clamp on the main.
*For flanged or mechanical joint tees remove the valve and install a blind flange or mechanical joint plug.
*For push-on tees, the tee, valve and thrust restraint must be removed and the main repaired with approved pipe and suitable couplings.
*Valve boxes for abandoned valves must be removed.
*Pipes twelve (12”) inches and larger to be abandoned need to be removed or broken every fifty (50’) feet and filled with sand slurry. (Check City Standards)
*Where a fire hydrant is to be abandoned, the hydrant barrel, break off riser, and check valve are to be removed. Abandonment of fire hydrants must be approved by the Fire Department.

Connections
*A permit shall be obtained for each connection to the water system.