Leaking ball cock valve in loft water tank

If no water is coming out of the overflow but you're losing 167 litres, the leak may be from: - A hidden pipe leak – possibly under floors or in walls. - Toilet cisterns – a slow, silent leak into the bowl (check by placing toilet paper at the back of the pan and seeing if it gets wet). - Hot water cylinder or tank – it could be leaking into a drain or evaporating if in a warm loft. You should get a plumber or leak detection specialist to investigate, especially if it’s not visibly escaping.