When you pay for your water what do they charge you for?

[The_Blue_Dragon]

Hi people,
Yesterday I went to my stepdads and he told me something I cant understand. He told me he got his water bill and has been charged for the usuals tap water, sewage etc.

And then he said he get charged for when it rains When ever rains lands on his roof and falls to the floor he is charged.
Surly this is a load of rubbish? surly they cant charge you for that

 

[The_Blue_Dragon]

Im not messing and he really sounded serious.

He says they charge you because it runs down your drainpipes into there drain system?