What is backflow and why must we guard against it?


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?

By Patrick Gordon

Patrick GordonFirstly, 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?

Firstly, we need to take cognisance of the fact that once the water passes 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 could be viewed as potential contaminants?

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 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 so as 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 it from happening. The regulations are very clear on what is expected from us and how to achieve zero backflow from entering the potable system. A follow-up article in the October issue of Plumbing Africa will go into detail on how to achieve this.