An apartment water meter has been running high for the last three months for no apparent reason. It's now about 3,000 gallons higher than normal. The meter registers slow continuous usage - even though no fixtures or appliances are active. There are no signs of water leaking into the walls or floors.

Two professional plumbers have checked for problems with no success. We double checked toilets - the usual suspects - but one plumber determined that shutting off the HW feed to the HW Heater stops the meter. So I believe it's in the HW side of the apartment.

The only HW fixtures are only a couple of sinks, a shower, a dishwasher, and a clothes washer. All look fine.

The obvious candidate would be the HW Heater excess Temperature and Pressure safety valve - the "T&P" valve. But the outflow tube from that valve is bone dry.

One plumber suspects the meter. Could a water meter malfunction behave differently depending on whether the valve to the HW Heater is open or closed?

I'm starting to wonder if some fool connected the ice maker to the HW line. What could it be? Any suggestions to isolate the culprit?

  • Water softener is my usual suspect after toilets - I suppose if it's plumbed only on the HW side (as is sometimes the case) that could still be it, but you don't mention one, so you may not even have one.
    – Ecnerwal
    Oct 13, 2018 at 15:15
  • 1
    3000 gals. is a lot of ice... check for under-slab leaks, professionals have detection devices for this. Listen to the pipe with a stethoscope, for flow. I have seen meters click off as if there was flow due to water surging back & forth too... Oct 13, 2018 at 16:50
  • Sprinkler maybe.
    – user19565
    Oct 13, 2018 at 17:09
  • what kind of heat does this apartment use, and what kind of hot water appliance is used? Perhaps there is a slab leak as suggested and "some fool" used the HW line to feed the closed loop boiler top off valve instead of fresh water cold supply. (presuming it may have one)
    – noybman
    Oct 13, 2018 at 18:02
  • It can be due to 'hot water recirculation' not properly plumbed. Anyway, usually meter are placed after the 'junction' between hot water 'flow' and return but in your case you can have the meter placed within the loop so you pay for all all 'recirculated' water as used water.
    – DDS
    Oct 13, 2018 at 19:14

1 Answer 1


Finally resolved this one. It surprised everyone. The apartment had a HW Expansion Tank (required by code) but no check valve (the building has one, but individual units don't).

It turns out water was flowing through the meter into the HW expansion tank, then flowing back out - no net water consumption, just a few ounces of water cycling into and out of the expansion tank with changes in pressure. 3,000 gallons a month is about 9 ounces a minute.

But the water meter only advances in one direction, so it accumulated as usage. We installed a check valve and the problem was corrected.


  • 1
    It would be nice if you informed your neighbors of the situation you encountered and its solution, in case they too are missing a check valve. Nov 3, 2018 at 15:52
  • Good suggestion P. Freedenberg. The HOA is doing that.
    – jbbenni
    Nov 3, 2018 at 19:04

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