Drugs in the water supply

Here in the UK, we have a rule (it may even be a law, I’m not sure) that you don’t throw medicines, especially prescription ones, down the toilet or in the dustbin. We are told to return them to the chemist or pharmacy we got them from.

What they then do with them, I haven’t a clue.

And of course, that is no answer to the original question, about “natural” disposal into the system.