Pool Watch No. 7

I should, I suppose, have marked the water level in the pool yesterday evening after we'd all got out of it. Otherwise how could I check the extent of the water loss. The reason I didn't make a mark is that I actually expected to find no water whatsoever. I've just been out and there's actually quite a bit still in there - possibly even exactly what went in yesterday.

Seems there isn't a leak, but where the hell did the water underneath come from?