Water Facilities & Systems

Is Emergency Power Required for Water Distribution System Facilities?

The requirement for back-up power for distribution system facilities is driven by 3 Arizona Administrative Code (AAC) requirements as follows:

• R18-5-502.B - A potable water distribution system shall be designed to maintain and shall maintain a pressure of at least 20 pounds per square inch at ground level at all points in the distribution system under all conditions of flow.
• R18-5-503.A - The minimum storage capacity for a CWS [community water system] or a non-community water system that serves a residential population or a school shall be equal to the average daily demand during the peak month of the year. Storage capacity may be based on existing consumption and phased as the water system expands.
• R18-5-503.B - The minimum storage capacity for a multiple-well system for a CWS [community water system] or a non-community water system that serves a residential population or a school may be reduced by the amount of the total daily production capacity minus the production from the largest producing well.

Item 1 Conformance

Conformance with item 1 is usually implemented by the construction of one or more reservoirs to provide storage capacity for a distribution system service area. Properly designed reservoirs located at the high water elevation of a service area can provide hydraulic head to maintain a nominal system pressure of 20 psi. In some cases, isolated service areas may be fed by redundant supply sources instead of using reservoirs to maintain system pressure.

Items 2 & 3 Conformance

Conformance with items 2 and 3 is implemented by calculating the size of the reservoirs to provide sufficient capacity to meet the required capacity for peak and fire flow demands in combination with redundant supply sources feeding a distribution system service area such as surface water treatment plants, groundwater wells, booster pump stations and pressure reducing valve stations.

Emergency power may be required for groundwater wells, booster pump stations and pressure reducing valve stations acting as a source of supply to isolated service areas. For example, a service area with insufficient storage capacity fed by two other service areas via booster pump stations that are on the same electrical grid would not conform to the AAC requirements as loss of power would result in a loss of pressure in the distribution system.

An engineering analysis should be performed whenever a water distribution system is being modified or expanded to determine if emergency power is required for new or existing groundwater wells, reservoirs, booster pump stations and pressure reducing valve stations. The analysis should calculate the required minimum storage capacity for peak demand and fire flows and address the impact of system wide interruptions due to loss of power, major transmission pipeline ruptures and equipment failure.

What Are the Disinfection Requirements for Commissioning Piping or Equipment in Potable Water Service?

Arizona Department of Environmental Quality (ADEQ) Bulletin No. 8, "Disinfection of Water Systems (PDF)," specifies the methodology and requirements for the disinfection of new piping and equipment. Bulletin No. 8 also discusses disinfection using chlorination as well as safety measures and emergency disinfection procedures.

In addition to the disinfection procedures specified in ADEQ Bulletin No. 8, the following American Water Works Association Standards may be used:

• AWWA Standard C651-05 - Disinfecting Water Mains
• AWWA Standard C652-02 - Disinfection of Water Storage Facilities
• AWWA Standard C653-03 - Disinfection of Water Treatment Plants
• AWWA Standard C654-03 - Disinfection of Wells

Disinfection Verification

To verify effective disinfection, bacteriologic samples must be collected from the same locations at the time intervals and frequency specified by the above standards. The samples must be analyzed by a laboratory within 24 hours of collection of the sample. Samples should be maintained at or near 4°C until they are sent to the testing laboratory for testing.

When the laboratory provides written confirmation of the absence of total coliform bacteria in all samples, the piping or equipment is considered to be disinfected. If any of the samples fail, the disinfection process shall be repeated per the above standards until the samples pass.

Water shall not be sent to the distribution system until:

• The piping or equipment has been disinfected.
• Certified copies of the laboratory analysis reports have been submitted to the Subdivision, Infrastructure and Planning Program.
• Written authorization (signed Approval Of Construction) approving the release of water to the distribution system has been received from the Subdivision, Infrastructure and Planning Program.