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,