Water meter - backwards when stopcock off

[dormermike]

Hello

We have a small ground floor utility room (2m x 2m) and its go an old (1990's) solid concrete floor, likely no DPM in place. Noticing odd damp patches, e.g. under vinyl flooring.

The room has a lot going on - incoming water main (MDPE) with very recent lever ball valve stop cock, incoming gas, boiler with condensate, drainage pipe for bath in adjacent bathroom, washing machine, and all the incoming electrics. External wall, ground level outside decently below DPC, cavity wall, and no window.

Suspecting a small water main leak beneath the floor, i turned off the stop tap for an hour and recorded the meter (which is in the street). The small needle (not the digits) moved very slightly, i mean almost imperceptibly slightly, backwards.

Does this mean that there is a leak in the pipe? I was expecting it to go forwards if there is a leak between the meter and my stoptap, not backwards. As i say, it was very very small amount of movement on the tiny needle, no movement on the digits.

Perhaps i should run the test for a few hours and see if i get different results or is an hour usually enough?

Otherwise, i think i'm looking at DPM issues (or lack of) but, we recently had the opportunity to inspect inside the cavity (old boiler exhaust removed) and it was bone dry at the bottom near the water main which is in the corner of the room.

thanks
Mike

 

[Elkato531]

A leak down stream of the meter would result in water passing through the meter and a forward movement of the dial. Only reason I can think of for backward movement would be thermal expansion of water in the pipe if its warmer under your floor than in the water main. This would only be a tiny amount though. Doesn't sound like a leak.

 

[alphagario]

Maybe condensation

 

[dormermike]

Thanks, that's sort of what I was thinking too.


I forgot to mention I've had a dehumidifier running in there and it's pulling loads of water out. We did have a leak under the shower in the adjacent bathroom but that has all be ripped out and is currently just bare concrete, and dry. It was leaking badly for many years, so perhaps im seeing excess moisture still making its way through the slab. Seems a stretch.



Oddly, the cat got in there and peed over the stop cock which is highly unusual for him. That was weeks ago though, and a one off.



Another cause could be excess humidity and a cold slab, aka condensation. I plan to add an extractor which may help.