Odd water meter issue

[Newman]

I'm in the process of a remodel, and we just put up drywall. Plumbing, both main and inside, is all brand new (Uponor). Water meter is 1" Neptune T-10, digital readout.

I just started checking the water meter a few times a day to make sure everything was fine after drywall - and yikes, I show flow even though everything is off. I've been testing everything the past few days, and bottom line is I can't find a single leak. Moisture meter across every wall where pipes are located, nothing. The system is split up into 4 zones, and all will show anywhere from 1-7 gallons of water over a 12 hour period. Turning off all zones will cause the water meter to remain steady.

To further test, I shut off the main and internally raised the pressure of all zones to 80 psi with air, and it's holding steady after several hours, which seems to suggest there aren't any leaks in the system.

So why in the world would the water meter be incrementing!?

The water meter never shows any flow (with the digital arrow), it appears to be small changes or periodic fluctuations that add up to several gallons a day. I did see one time where it actually went *down* briefly, leading me to think there is some backsiphonage to the main.

There's no backflow device installed right now (no sprinklers connected). My only theory is that somehow the water is flowing back and forth across the meter due to the pressure changes (we're at the end of a small main, with around 30-40psi), and the meter is incrementing rather than just netting everything out. This only happens when zones are opened up, creating the back pressure as most of them are on the 2nd story, and thus creating illusion of a leak.

Obviously the next step is to install a backflow limiter and see if that stabilizes everything

I was just curious if anybody had any experience with meters and their accuracy. Hard to imagine the water meter is actually flawed, but I'm stumped otherwise.

 

[Scott580sm]

Are you living in the house? If possible, put a pressure gauge somewhere in your system. Turn the water off at the meterset and see what the pressure does over a 24 hour period. It takes much less water loss to see a pressure drop than it does air. If everything holds, should be sufficient evidence that it’s in the metering. Neptune’s data says a 1” meter is only 95% accurate at 3/8 gpm. Weird things can happen with a water system. You mentioned being at the end of a small main. It’s possible when other people are at a high usage you’re bleeding back into the system at a slow enough rate that the meter doesn’t run backwards fast enough to register. When everyone shuts off, the surge from the pressure building back up causes a usage reading. Make sure with a backflow you put in some kind of expansion tank. Seen a few water heaters spring leaks because there’s nowhere for the heated water to expand to when it can’t go backwards.

 

[Sponsor]

 

[Scott580sm]

 

[Newman]

Yup - just in case anybody else ever runs into this, a basic double check valve has caused the meter to work properly. The pressure fluctuations on the main line definitely caused the meter to overreport flow of around 3-4 gallons/day.

Pardon my ignorance, but I'd never heard that the lack of a backflow preventer could cause the meter to actually overreport water useage. The previous owner obviously didn't have one installed (it's only required on the irrigation branch here). I'm surprised the water company isn't more up front about this, and at least recommend backflow preventers for everyone.

I guess 1000 gallons extra/year isn't a lot, but what stymied me was thinking this was a leak. If you don't have a backflow device after the meter, don't assume the meter is perfectly accurate for small leak detection.