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What is backflow and how must we protect against it?

VALVES

The movement of any substance in any direction is called flow. So why the term backflow when water moves from an installation towards the municipal potable supply? Firstly, it is assumed that the water in any installation originates from the municipal supply and so the water that flows back towards there is viewed as flowing back and thus called “Backflow”. In most instances this would be the case, so why would we need to guard against it? What has happened to the water that makes it unsafe to return it from where it comes from? Firstly, we need to take cognisance of the fact that once the water passes past the water meter it now becomes the responsibility of the homeowner and the municipality no longer has control over what happens to it. Once they have lost control over what happens to the water, they do not want to let it back into the municipal system. We could let the water back into the municipal system if we had it tested and certified as SANS 241 quality compliant, but we know that that is not practical. What do we do to the water that could be viewed as contaminating it? • We often have water softeners on the supply to the home and this is done by adding chemicals to the water. • The water is often heated in an aged Hot Water Cylinder that will add limescale to the potable water in a backflow situation. • When summer comes and we are filling the pool and fishponds with a hose this could also be a cause of contamination.

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Pipes, Pumps and Valves Africa - May/Jun 2021

So, if we look at it from their view the probability of getting contaminants from domestic installations is very high and we have not even ventured into the water from alternative sources such as boreholes and rainwater harvesting. Thus, it is no wonder that SANS10252/1 of 2018 says in D.1.1 Design, installation and maintenance. All water supply systems shall be designed, installed, and maintained to prevent contaminants from being introduced into the potable water supply system. The big question now is not the quality of our water but how to prevent backflow from happening. The regulations are very clear on what is expected from us and how to achieve zero backflows from entering the potable system. In terms of the National Regulations, SANS10252 -1 (water supply installations for buildings) refer to 7.4 of SANS 10252-1 ‘Preservation of Water and Water Quality. Reduced Pressure Zone Back Flow Preventers must be installed in any installation where there is a risk of contaminated water or harmful substances being back syphoned or flowing back into a potable water supply line. The regulations state that Back-flow Preventers shall be installed in certain types of installations and buildings, for example:

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Pipes, Pumps & Valves Africa May/Jun 2021  

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