Disinfection procedures for water mains and services

Pathogenic (disease causing) organisms live in the soil and the disinfection of water mains is a vital preventative step for the supply of safe drinking water. An independent certifying consultant must certify as witness to the below procedures.

1. A chlorination test must be conducted and results recorded. The constructor may conduct the chlorination test in accordance with the below method, using calibrated chlorine testing equipment.

2. An accredited National Association of Testing Authorities lab must be contacted to conduct the bacteriological tests. Power and Water project officer and/or auditors need to be notified a minimum of two working days prior to all testing and collection of test samples.

3. Constructor to ensure that the connection to the existing main is installed prior to construction of the new reticulated pipework. At no stage must any contractor remove the valve lock or in the event where there is no valve lock, operate the sluice valve of any live water main. Power and Water employee will open the sluice valve on the existing water main only after acceptance of the new reticulated pipework. For services larger than 50mm - Power and Water personnel must install a valve lock on the sluice valve to the new water service.

4. Ensure pipework and fittings are cleaned (e.g. remove mud, spray pipe fittings and materials with hypochlorinated water) prior to constructing new water service.

5. Pressure and chlorination testing can be combined to reduce time taken for commissioning.  Sodium hypochlorite solution should contain 12% chlorine by weight. This concentration will degrade with time and high temperatures. Use sodium hypochlorite only and ensure that it is less than a month old.

6. Flush the new water pipework at high-flow using mains water through an approved Power and Water meter with the appropriate backflow prevention device to remove debris. NOTE: The constructor can flush with potable water from Power and Water’s reticulated water mains through an existing fire hydrant or through an existing property service connection, using a construction water meter with a backflow prevention device connected.

7. Combine and evenly mix the required amount of water and chlorine into the new water pipework to achieve a minimum chlorine concentration of 25mg/L (ppm) and maximum concentration of 100mg/L (ppm). The apparatus used to mix must be disinfected prior to use. For services between 20mm and 50mm – Chlorine levels need to be measured to confirm concentration in the new water service. Chlorination is only required to be held for the duration of the pressure test. Ensure pipework is flushed out after the test. For services larger than 50mm and subdivision mains – A full 24 hour chlorination test needs to be conducted (Steps 8 to 14).

Disinfection steps (8-14) for services larger than 50mm and subdivision mains

8. Collect a sample of the chlorinated water being used to super chlorinate the new pipework. This water sample will need to be tested for chlorine and the test result recorded.

9. Leave mixed chlorinated water in the new pipework for a period of 24 hours.

10. Collect a sample of the chlorinated water pipework after 24 hours. This water sample will need to be tested for chlorine and the test result recorded.

11. Ensure that at least 10mg/L (ppm) of chlorine is achieved after the 24 hour period. If the test does not achieve the minimum chlorine levels, repeat method from step 6.

NOTE: Clean pipework will not degrade chlorine to less than 10mg/L.

For services larger than 50mm - The chlorine levels must be tested again by the same certifier to confirm concentration level is achieved.

Test procedure - bacteriological tests and de-chlorination (services larger than 50mm and subdivisions)

12. After successful completion of chlorination process, adequately flush the new water main at high flow as per step 6 until chlorine residuals are equivalent to town water (less than 1 mg/L). Power and Water must be notified a minimum of 24 hours prior to flushing. The certifying consultant must collect and deliver the water sample for bacteriological test. The table below is the water quality parameter limits of a bacteriological test.

Water quality parameter limits

*For Cement mortar lined mains an upper level pH of 9.2 is acceptable.

13. The consultant must provide the successful pressure, chlorination and bacteriological results to Power and Water prior to the handover meeting. The chlorine results will only remain valid for a maximum period of 30 days from date of testing.

14. Once tests have been completed and to the satisfaction of Power and Water requirements, the chlorinated water must be discharged to prevent damage to pipe lining or prevent corrosion to the new pipework. The environment to which the chlorinated water is to be discharged must be inspected and approved by the relevant authorities. If chlorinated discharge may damage/affect the environment, neutralising chemicals must be used.

(After completion and acceptance of works, Power and Water will remove the valve lock and make live the new water service.)

NOTE: The following table can be used to calculate with 12% Sodium hypochlorite solution.

A copy of the Water Test report can be found here