I recently bought my first house. It's come with it's share of issues, such as doors coming off the hinges, ones that don't open, dodgy dimmer switches, my partner setting fire to the kitchen and large holes in the wall to outside.

Now I'm looking at water. We're on a water meter which is why I noticed, but we were using about 10 litres of water overnight. Taps don't appear to be dripping (left plastic bags underneath and not wet in morning) and the boiler (combi type, no hot water tank) is switched off so I wouldn't imagine it's using anything but I don't know how they work.

I isolated the upstairs toilet after noticing it making filling sounds from the tank when it shouldn't and that cut it down to about 2-3 litres of water overnight.

I isolated the shower heads and about half the taps (bath taps don't have visible isolation valves, hot bathroom sink valve is inaccessible, cold kitchen sink isolation valve is accessible but leaks when set to closed, but not when set to open oddly, not sure how to isolate water into boiler as can't see any isolation valve on pipe).

Can anyone suggest what might be causing the water loss or make any suggestions on searching for leaks?