is it illegal to catch rainwater in the uk
The installation of rainwater harvesting systems in the UK should be done according to the Water Supply (Water Fittings) Regulations and BS8515, in order to ensure safety. BS8515 also provides details on how to size the storage tank and allows estimation of the potential water savings. If you install a RWH system, you will need to inform your water company.
Rainwater harvesting in the United Kingdom