Why do mains water pipes never need cleaning?

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If you’ve worked in a bar you know the relatively short connection between cellar and bar needs frequent cleaning.

So why does the connection and internal pipes in your home never require any cleaning, despite providing potable water?

I’m aware that throughput in the pipe an chlorination play a role, but working in a new hospital plagued with legionalla it’s amazing to think my Victorian house is ticking away with decades old pipes without an issue.

In: Biology

There’s chlorination but most water systems will add a small amount of something called orthophosphoric acid. This acid is a pretty benign acid and is used frequently as a food acid. As it passes through the mains pipes it reacts with the metal of the pipe to form a layer of metal phosphate. This metal phosphate layer is highly resistant to things growing on them and sticking to them. It also prevents any future corrosion of the pipes below the surface of the phosphate layer.

Also the pipes are always kept under pressure. Even if there’s a leak into the environment from the pipes, water is always flowing out of the leak, nothing can get back in.

“Bugs” or pathogens (things that can do us harm), by which I mean bacteria an viral contaminants, typically need oxygen to thrive, or in the case of “anaerobic” pathogens, they at least need a source of food, such as with waste products. Potable water has neither in the delivery pipes, at least until you get to the end where it comes out. So when the water is treated BEFORE it goes in the pipes, any pathogens are removed or killed, then anything that might make it through has nothing to live on and dies along the way. You DO have to be careful with the spigot in your house and most people are, but that’s why you should NEVER put your mouth directly on the spigot or let your kids, friends or pets do so. Outdoor pipes such as sprinkler systems and fire suppression pipes typically have what’s called an “anti-siphon” valve that will prevent any potentially contaminated water from getting drawn back into the pipe system.