Page 11: Guidance For Providing Safe Drinking Water in Areas of Federal Jurisdiction – Version 2

Appendix E: Distribution System

Table E.1 Investigation of water distribution systems (InfraGuide, 2002)
Problem Preliminary assessment Detailed investigationFootnote 1
Structural condition
  • Spatial and temporal analysis of water main breaks
  • Compilation of soil map
  • Routine inspection of valves and hydrants
  • Routine inspection of insulation and heat tracing in northern areas
  • Detailed analysis of break patterns, rates and trends
  • Statistical and physical models
  • Pipe sampling
  • Soil corrosivity measurements
  • Pit depth measurements
  • Non-destructive testing
  • Failure analysis
  • Visual inspection
  • Thermal analysis (far north)
Hydraulic capacity
  • Low-pressure complaints
  • Hydrant flow tests
  • Unusual rusty/coloured water occurrences
  • Visual inspection of pipe interior
  • Monitoring of pressure and pumping costs
  • Hazen-Williams C factor tests (pipe roughness)
  • Computer modelling
Leakage
  • Water use audit
  • Per capita water demand
  • Routine leak detection survey
  • Leak detection survey
  • Detailed limited area leakage/demand assessment
Water quality
  • Water quality complaints
  • Routine sampling data
  • Results of flushing program
  • Detailed water quality investigation
  • Computer modelling

Some distribution system-specific definitions

Vacuum breakers

Vacuum breakers are used to prevent backflow of water into the distribution system. These include atmospheric, hose bibb, and pressure vacuum breakers. These devices can provide protection against back-siphonage (the flow of water into the potable water system pipes caused by the sudden reduction of pressure in the potable water supply system) but should not be used to protect against back-pressure (when a facility's system pressure is greater than the supplier's system pressure) conditions (U.S. EPA, 2003; NRC, 2010). The selection, installation, maintenance and repair of these devices is to be done in accordance with Standard B64.10.01.

Valves

Valves are important devices in the distribution system. Their purposes include turning on, shutting off and regulating flow; providing air or vacuum release; and reducing pressure.

Isolation valves are the most common type used in distribution systems. Buried gate valves with valve boxes are typically used to isolate small-diameter water mains and water services, whereas butterfly valves are direct buried or installed in chambers and are typically used for large diameter mains. Isolation valves require regular exercise to ensure they are accessible, are in their proper position (open or closed), are operable and not leaking. Isolation valves are prone to deterioration and failures such as stripped, broken or bent stems; leaking O-rings or packing; corrosion of the valve body and connecting bolts; and wear on the valve disk and seat (InfraGuide, 2002).

Water storage

Ground storage reservoirs are large tanks made of concrete or metal located at ground level. Concrete tanks are usually buried to prevent freezing of their contents. Metal storage tanks, when used, are insulated and may have a steam line running from the boilers to keep them ice-free. Recirculation of water from top to bottom of the tank will minimize the heat required.

Elevated storage is provided by means of standpipes or tanks. As elevated storage is more difficult to keep from freezing, especially the water in the riser to the tank; steam or hot water lines can be installed in the riser and the riser can be insulated.

All reservoirs are to be covered to prevent contamination and pollution. The covers also safeguard against drowning. Covered reservoirs or tanks must have air vents to allow air in and out as the water level is changed and these vents must be screened to keep out insects and small animals. Access manhole covers are to be provided for cleaning and inspection purposes.

The security of water storage reservoirs is an increasingly important issue. Federal water reservoir access covers are to be locked and secured at all times (DND, 2007).

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