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I realized that the leak indicator of my water meter ever so slightly moves back and forth. This is problematic because I attached a magnetic field sensor to measure the water consumption (and use it for leak detection). But since the disk always slightly moves, it always records a water flow. Furthermore, I find it very concerning that there doesn't seem to be any backflow preventer from my house to the public utility line. It seems I can just push back (possibly contaminated water) into the public utility line! Doesn't feel right to me.

This figure shows the configuration of my water heater (just recently installed):

enter image description here

I made a test and closed the valve (V) that goes to the water heater. Now the meter behaves as expected: The leak indicator does not move any longer and the measured magnetic field stays constant (indicating a quiet nutating disk).

I am not sure about the exact cause but I assume the how water leaks through the mixing valve (M) into the cold water line and causes pressure variations there which pushes my water back into the public utility line.

  1. Did my plumber forget to install a check valve or backflow preventer? Is it required in California?
  2. If not required: Why not? I feel there is high risk that people may inadvertently contaminate the public utility line
  3. Where are the right location(s) for check valve(s) / backflow preventer(s)?
Triplefault
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divB
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2 Answers2

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Yes you need a check valve.

Do you have a pressure regulating valve? The check valve is typically installed right after the PRV.

Yes you could push back contaminated water.

I've heard the water meter will register backward flow and count it against you.

Thermal expansion will certainly push water back into the city supply without a check valve.

Fresh Codemonger
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2

Not here, it isn't

The California Plumbing Code and its parent Uniform Plumbing Code, as well as the International Plumbing Code, take a point-of-use approach to mandatory backflow prevention, as their goal is to protect not only other water users, but people in the same building as a potential backflow hazard. As a result, they do not require backflow prevention at the water service entrance, and without anything to check expansion back into the water line, you get the phenomenon you are observing.

The good news is that this backflow situation is essentially harmless since the water put into the water heater was potable to begin with, and generally won't stop becoming potable after being heated. (If the contents of your hot water heater aren't potable, then you have bigger problems.) To your concern about pushing contaminated water back into the utility supply, though, the solution is to make sure your points of use are protected properly, including irrigation systems and hose bibbs.

ThreePhaseEel
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