I should have mentioned some ...

I should have mentioned some of the legislation relating specifically to water resources used for drinking water supplies, since you mentioned it. The most important piece of legislation was the 1963 Water Resources Act, which created the need for abstraction permits, the purpose of which is to protect downstream users of water resources. In the UK we do not have water rights as in the USA, which treat water as property. In the UK, nobody "owns" water - they are only able to use the water if they have an abstraction permit or a riparian right of use for non-consumptive purposes. Once we became part of the EU, we had a requirement to form river basin agencies and to produce water resources plans, but these were already in place as a result of the 1963 Water Resources Act, which also created River Authorities organised on a river basin basis.