Best-practice
BACKFLOW PREVENTION Given the potential for any backflow situation to cause sickness or even death, a backflow prevention device should be used on every water supply connection, says Haydon Mace, Technical Lead at Hydroflow.
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hilst you’ll rarely hear a true Kiwi complain about long, hot summer days, in recent years the soaring temperatures and lack of rainfall have resulted in the need to conserve water. With water at a premium in places like Auckland, Marlborough and Hawke’s Bay, the importance of protecting what we have has never been higher.
Back-siphonage and back-pressure Backflow prevention is a key component in maintaining the availability of highquality drinking water and fits neatly into the Government’s Three Waters Reform Programme. There are two distinct types of backflow situations: back-siphonage and back-pressure. When foreign contaminants are introduced into a potable water supply due to back-siphonage or back-pressure, we call this backflow. Back-pressure situations arise when the downstream (delivery side) of a water supply has a higher pressure than the upstream (supply side); this may be due to a downstream pump forcing water back upstream through the pipework. Backsiphonage occurs when the supply pressure drops to less than the atmospheric pressure, inducing a siphon through the pipes. Backflow prevention devices are classified as low (nuisance by colour, odour or taste), medium (potential to injure or endanger health) or high hazard (potential to cause death). The main objective of a backflow prevention device is to protect drinking water from being contaminated. And it’s not just industrial manufacturing
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companies in big cities that are at danger of contaminating the water we drink. The danger we face from unhealthy water can be greater than we think.
A common dangerous scenario Mixing chemicals with water using a hose is one of the most common, dangerous causes of backflow conditions around the world. In the above scenario, if there is a drop in supply pressure (before the hose tap) then back-siphonage will occur, sucking the poisonous chemical out of the container and into the household water system. This could also travel into the town supply water main and affect other homes. When it’s that simple to potentially poison your family, neighbours and community, it makes sense to take a best-
Recommended installation of hose bib vacuum breaker
Stainless steel double check valve for medium hazard situations.
practice attitude towards eliminating the potential harm. In this case a few simple steps are all that’s necessary: Don’t leave an open-ended hose inside chemical mixing containers Do install a hose tap vacuum breaker on the outlet of the hose tap, before the hose adapter or hose tail. These are low cost, high hazard protection devices that will create an air gap as soon as a back-siphonage situation arises, preventing the chemicals from entering the water supply.
Havelock North water contamination
ABOVE: Mixing chemicals with water is one of the most common, dangerous causes of backflow.
The above example is simple and easier to foresee than some other potential backflow situations, such as the events that took place in Havelock North back in August 2016. Scenes on our TVs showed families queuing by water tankers with large plastic containers—something that we shouldn’t expect in our ‘100% Pure New Zealand’.
