I noticed a round metal cover in our loo this morning, its approx 5 inch diameter. I've lifted it and there's rusty looking water water in it, it could be water that's leaked into it because it doesn't seem to go anywhere and flushing the nearby loo has no effect. If I prod with a stick it's about a foot deep and there seems to be another cover as there's a metallic thud.
I'll have to get the water out to investigate further but any ideas? Water meter?