After using 100m^3 extra water last year, I installed a Raspberry Pi with a camera to look at my water meter. Soon it will be able to cut off the water on excessive drain (like a forgotten garden hose). I have stopped the toilets leaking, and now I'm down to losing about ½liter per hour. It is on the hot water (shower) circuit, If I close the hot water, no drain. Each little blip on the graph is 1/8 turn of the 1l dial on the meter, i.e. 0.125l. Here the hot water is turned off at 11:20
It must be under the floor. In the bathroom (but the plumbing is in the wall) and the boilerroom, the floor is tiles on top of concrete, then some isolation. In the kithen I believe is (from bottom) earth, concrete, insulation, chipboard, floorboards, but the pipes just comes in from the boilerroom, then up to the sink.
It can't be upstairs; a bucket of water would be noticed. If I just monitor the loss, and it does not get worse, is it worth going through the concrete to find this small leak?
The software is an adaption of https://blog.m.nu/vattenmatning-med-raspberry-pi-och-webkamera/ in Swedish, I'm afraid.
I could put it on github I guess...
There is a gap between the pressure valve outlet and the drain, but I have left a cup there for 15 minutes, and it is completely dry.