Fact Sheet 8, Drinking Water Quality Assurance Rules 2022
Storage and Distribution
The transmission of water from the treatment plant to the various consumers is done in two stages, storage and distribution / reticulation. The integrity of a well-managed distribution system is one of the most important barrier that protects drinking water from contamination.
The distribution system requires some monitoring and testing for key parameters, disinfection by-products and plumbosolvent metals. It also requires a backflow prevention programme, as well as monitoring and testing of devices.
Preventative measures should be taken to ensure your treated water does not become contaminated. These measures should be developed when preparing your Operations and Maintenance Manual.
Storage Tanks
Storing water helps to:
- Buffer the demand of water against the ability for the system to supply it.
- Maintain uniform pressures in the distribution network.
- Provide a reserve for emergencies that might impact on the supply. Because water quality can degrade if it is stored too long, you will need to monitor the tank storage water levels and volumes and know the alarms and action levels to respond to for these parameters.
Operational inspections and preventative measures for your storage tanks include:
- Installing screen.
- Ensuring tanks are covered, sealed, lightproof and ventilated.
- Ensuring the draw-off point for taking water from the tank is above the base of the tank.
- Inspected and cleaned at least every two years.
- Sensors, such as those measuring the water level, will need to be either calibrated or regularly replaced.
As for treatment systems, a plan needs to be in place for shutdown, outage management, as well as fault and incident response.
Distribution Systems
The distribution system takes the treated water and delivers it to your consumers. Drinking water distribution systems need to be operated in a coordinated way so that adequate pressure, residual disinfectant and flows are maintained, and pressure surges, contamination and leakages are avoided.
Preventative measures for your distribution system include:
- Water from any overflow pipes should not be allowed to pool or stagnate.
- Buried pipes should be installed away from, and shallower than, septic tanks or wastewater pipe work.
- Pipes that are not self-draining (e.g., half syphon downpipes) should be drained every six months.
- Monitor residual disinfection levels and water quality determinants within the distribution network.
- Water quality complaints shall be recorded and analysed.
- Sudden increase in demand or high demand in the middle of the night, can indicate a leakage, or alternatively illegal connections, posing a risk to your supply including backflow.
- Regular cleaning, (e.g. flushing, scouring or pigging the mains) is important if you distribution system is prone to collecting sediments, biofilm growth or has a history of dirty water complaints, or odours.
When there is a problem with the distribution system, you will need to follow your incident and emergency plan to resolve the issue as soon as possible (e.g. pipe burst, or leakage) and communicate with customers about any impact.
Backflow Prevention
Backflow, from a customer’s property back into the distribution system, is a public health risk. It can occur when the pressure in the distribution system drops below the pressure in the customer’s property.
Backflow prevention devices help to prevent the reversal of flow from occurring. They must be appropriately selected, installed and tested to successfully protect the drinking water distribution system from backflow contamination.
Testable backflow devices are usually installed on higher risk connections, with untestable backflow devices usually installed on lower risk residential connections.
If water is extracted from bores, or you supply water carriers, you will also need to address these unique backflow risks.
New customers also need to be assessed for their backflow risk before connecting them to the system. Water from any overflow pipes should not be allowed to pool or stagnate.
More specifically, you need to:
- Determine if a connection is a low, medium or high risk for backflow.
- Determine what type of backflow preventer is suitable for certain customers.
- Regularly review the risk of backflow on the distribution system.
- Keep records about backflow risk and inspections system from the properties/connections that you supply water to.
- Carry out appropriate maintenance, replacement and calibration and keep records.
All New Zealanders need access to SAFE drinking water.
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