Water Meter Going Backward

[tranelch]

Shortly after finishing construction on our new home, the utilities company called to question our meter reading. Through experimentation with the department of public works, we discovered that sometimes when the outdoor spigots (water only meter) were running, the indoor meter (water and sewer) would turn backward. We never had air in the pipes, so we concluded that the meters were installed so close to the supply "T" (see attached photo), the turbulence was causing the meter to turn backward (in addition, if water was actually flowing backward, it would have to go back through the meter and would cancel out the backward flow). When I relayed our conclusion to our plumber, he responded that:

The check valve will actually be installed on the vertical pipe before it tees off...This is something that is not covered under our warranty because there is absolutely nothing piped wrong. ...The negative static pressure is not related to the plumbing system, but instead is caused by the city.

That just didn't make sense to me (the negative static pressure comment, if I understand it correctly, would suggest that the head pressure is pushing harder than the supply to the house when the outdoor spigots are running--we know that water is not flowing out through the meter), and I was not convinced that paying to install a check valve on the supply before the "T" would solve our problem. I then asked another local plumber to have a look at it. He agreed that the meters were too close to the "T"

I am wondering if the unbiased folks on this forum could break the tie and share there opinion on what is likely causing our meter to run backward.

Thanks in advance,
Chris

 

[tbart16]

wow that is crazy! I would install a check valve between the tee and the reversing meter. Good luck

 

[majakdragon]

Very strange situation. The Water company I worked for had geared meters that could not run backwards. If your meters allow reverse movement, you need two check valves, one installed before each meter. One, on the vertical pipe will not deter the situation.

 

[Reedwalker]

It is piped improperly.

Those meters are installed in a "series" and should have been installed in "parallel".

The flow rate from your irrigation system is so great it is causing turbulence and turning the gears of the meter. If the meters were piped parallel instead of in a series the flow would not even be close enough to do so.

The simplest fix is to install vented dual check between the two meters. This will allow any back flow or turbulence to be mitigated before it can affect the "main" meter.

I would also be sure your back flow preventor on your irrigation system is installed and working properly. You do not want to drink your irrigation water, and these systems are tied together in such a way that it would only take a small loss in city water pressure to create a backflow scenario. The ASSE recommends a RPZ (reduced pressure zone valve) in your situation.
sourced from the ASSE Residential Cross Connection Manual 4th Edition 2008

p.s. It's been my experience that metal clamps on plastic pipes are a bad idea. They expand and contract at different rates and can cause cracks. And I hate to nit-pick the guy, but why would you put a galvanized tee in between all that copper and brass. For three or four more dollars he could have used a brass tee and saved a future corrosion issue.

 

[tranelch]

Thanks for the detailed feedback everyone. It has been a crazy experience--I think the utilities company thought I was tampering until they saw the meter turn backwards themselves. If anyone else reads this, I would welcome more opinions as well--I have gotten such a wide variety of opinions, it would be nice to get closer to a consensus.

Chris

 

[majakdragon]

The only way to solve the problem is to isolate the meters from each other. The easiest way to do this is with check valves. This prevents flow to the unused meter while the other one is operating.

 

[SilverBack4Jack]

Definitely check valves before each meter. NOT just on the vertical line. 2 check valves not 1.

 

[ProFlowPlumbing]

I dont see how it could pull water from the source and also through the other meter,unless you have a booster pump on one system and/or an open faucet or a leak on your other system.Two check valves (one on each system) would be a good starting point ,and that would prevent cross connection contamination caused by backflow from your irrigation or hose bibs.

 

[meterman]

Hello i have been installing water meters for over 20 years i believe that your meter has been installed backwards by the meter installer.

 

[havasu]

I wouldn't be concerned, unless you were responsible for the installation of the water meter. My water company recently told me my meter had frozen up, and they needed to replace it. I asked how they would measure the previous month when the meter was frozen, and he said they would just use the average for the last 2 years. I sure wish I would have known this earlier because I would have had the greenest lawn and fresh water in the pool. Damn!

 

[Mr_David]

Lets say your water pressure is 60 psi.
You put a pressure gauge on a faucet or laundry valve in the house and turn on any other fixture you will normally get about a 5 psi drop in pressure.
The same if you open a yard spigot on the other meter. Some of that water in the house system will flow back to the opened yard spigot thus causing a reverse meter flow.
The large volume of water in the water heater helps feed that back flow. Makes sense to me. Check valve after the meter would probably work and easier to install
Having 2 meters , one for yard water and one for house water so they can bill you for sewer based on house water used is new to me but seems to be a good idea.

 

[mooseye]

I am assuming that the supply is coming up thru the tee then going left and right thru the meters. If this is correct, a check valve installed where the red arrow is will solve the problem. I can't believe 2 professional plumbers could not see the problem there.
It is very easy to see how opening the outdoor line would create a pressure drop and allow the water in the house supply to flow back, especially if the home water is mostly at a higher elevation.
It is hard to understand how there could be enough backflow for the utility co. to notice it. Even if it drained the whole system including the water heater, it should flow back and refill the system when the outdoor flow is stopped, thus counteracting any reversal of the meter.

[/IMG]

 

[barnabas1969]

I have to agree about the galvanized T connected to brass fittings AND about the metal clamps on the plastic pipe. Just plain dumb to use iron and brass/copper together... and it is against every CPVC manufacturer's installation instructions to use metal hangers/clamps on CPVC pipe.

As for the reverse flow... if you have an expansion tank on your water heater or somewhere else in the house, that would completely explain the backflow problem. You should definitely have a check valve.

 

[Plumber001]

Shortly after finishing construction on our new home, the utilities company called to question our meter reading. Through experimentation with the department of public works, we discovered that sometimes when the outdoor spigots (water only meter) were running, the indoor meter (water and sewer) would turn backward. We never had air in the pipes, so we concluded that the meters were installed so close to the supply "T" (see attached photo), the turbulence was causing the meter to turn backward (in addition, if water was actually flowing backward, it would have to go back through the meter and would cancel out the backward flow). When I relayed our conclusion to our plumber, he responded that:


That just didn't make sense to me (the negative static pressure comment, if I understand it correctly, would suggest that the head pressure is pushing harder than the supply to the house when the outdoor spigots are running--we know that water is not flowing out through the meter), and I was not convinced that paying to install a check valve on the supply before the "T" would solve our problem. I then asked another local plumber to have a look at it. He agreed that the meters were too close to the "T"

I am wondering if the unbiased folks on this forum could break the tie and share there opinion on what is likely causing our meter to run backward.

Thanks in advance,
Chris

I'm guessing you have a expansion tank on your water heater. When you use the outside spigot it will draw from both sorces untill the pressure equilizes.

 

[barnabas1969]

I'm guessing you have a expansion tank on your water heater. When you use the outside spigot it will draw from both sorces untill the pressure equilizes.

I completely agree. I had a similar issue. My issue was that there was no check valve at the meter, so surges in the city mains would cause water to alternately flow in and out of my meter. The expansion tank contains air that can be compressed, unlike water which cannot. This causes the in/out flow when the city mains change pressure. The city water pressure varies constantly by a few PSI, I assume due to fluctuations in demand.

The problem is that most meters aren't designed to run backward and don't measure reverse water flow correctly, so it was registering more in-flow than out-flow... resulting in higher water bills.

The city where I live has an on-going project to install check valves in older neighborhoods, but I didn't wait... I installed one myself. It fixed the problem immediately, and my water bill went down about $10-20 per month! That paid for the check valve in a hurry.

 

[Lou]

We do not have any expansion tanks. We did have a water leak, replaced all the piping and found now that our water meter is running forward (more so) and running back every say 30seconds. Overnight with absolutely no toilet flushing or taps turned on, the meter mover forward showing that 68 liters was used. With the total hours being 10.5, this means that over 24 hours and say 30 days, a total of 4.66 kilo liters was 'used'. Now this is a very expensive overcharge!
Reading all the previous comments, it would appear that we need to fit a check valve to avoid this problem from continuing. Any help or advice on overcoming this problem would be appreciated. My email address is [email protected] and we live in South Africa.
Regards, Louise

 

[mooseye]

We do not have any expansion tanks. We did have a water leak, replaced all the piping and found now that our water meter is running forward (more so) and running back every say 30seconds. Overnight with absolutely no toilet flushing or taps turned on, the meter mover forward showing that 68 liters was used. With the total hours being 10.5, this means that over 24 hours and say 30 days, a total of 4.66 kilo liters was 'used'. Now this is a very expensive overcharge!
Reading all the previous comments, it would appear that we need to fit a check valve to avoid this problem from continuing. Any help or advice on overcoming this problem would be appreciated. My email address is [email protected] and we live in South Africa.
Regards, Louise

If you are 1oo% sure you have no leak and no usage then you have a strangely defective water meter. A check valve would not help that. I would request that the water supplier come and check the meter.