The water regulations, and why backflow is the thing that matters

Amara Do I need to be registered to do plumbing in my own house?

Nadia For most domestic water plumbing, no. And that surprises people, because everybody assumes plumbing is like gas.

Amara So it is unregulated?

Nadia Not remotely. There is no registration requirement but there absolutely is law. The Water Supply Water Fittings Regulations 1999, and the byelaws in Scotland, apply to anybody who installs or alters a water fitting. Breach them and it is a criminal offence with a fine attached.

Amara What are they actually for?

Nadia One thing above all. Stopping contaminated water getting back into the drinking supply. Everything else in them is secondary.

Amara Backflow.

Nadia Backflow. And once you understand that it is the point, the whole rulebook stops feeling arbitrary.

Amara Then teach me the framework.

Nadia Five fluid categories. One is wholesome water as supplied. Two has changed in taste, smell or appearance but is not a health risk, so warmed water. Three is a slight hazard, a heating system with no additives, a domestic washing machine.

Amara And the serious ones?

Nadia Four is a significant hazard: inhibitor, antifreeze, pesticide. Five is the serious one, and it means human or animal waste or pathogens. A WC. A bidet. A trough. A sink you have been cleaning in.

Amara How does the protection change?

Nadia It rises with the category, and at category 5 you need the one protection that cannot fail mechanically. An air gap. A physical vertical gap between the outlet and the highest the dirty water could ever reach.

Amara Why not just fit a good valve?

Nadia Because a valve is a mechanism, and mechanisms fail. Grit, scale, age. An air gap is a piece of empty space and it has never failed in the history of plumbing.

Amara Give me the everyday example, because this still feels theoretical.

Nadia Your outside tap. Hose screwed on, other end lying in a water butt, or a pond, or a bucket you have been washing the car in.

Amara That is most houses in Britain.

Nadia It is. And that is a direct path from category 5 water into the drinking main, waiting for a pressure drop.

Amara How would the water go backwards though? It comes out under pressure.

Nadia Until it does not. A main bursts down the street, the pressure drops, and the system siphons. That is not a hypothetical, it is exactly how contamination incidents happen and why undertakers care so much about it.

Amara So what does that outside tap need?

Nadia A double check valve, which is two check valves in series and protects to category 3, plus the discipline not to leave the hose end submerged. About eight pounds of fitting, and it is the most common breach in the country.

Amara Is there anything I have to tell the water company about before I do it?

Nadia Yes, and people miss this. Certain work must be notified in advance and they can refuse consent. A bidet with a flexible hose. Any garden irrigation system. A pond or pool over ten thousand litres. A bath over two hundred and thirty litres.

Amara A big bath needs permission?

Nadia It does, because of the draw on the main. It catches out a lot of bathroom installers doing a high end job.

Amara Last thing. Fittings.

Nadia Use ones approved for potable water, so WRAS approval or another recognised UK scheme. And fit an isolating valve at every appliance, because the next person to repair it will otherwise be draining the whole house, and quite often that next person is you.