United Utilities have been doing these doorstep sample tests for quite a long time. They've been to me twice in about 15 years - maybe because we're nearby (10 miles away) so it's easier.
I'm happy to use tap water for cooking etc. and used filtered tap water for the kettle and to add to squashes etc., only because our water can sometimes taste of TCP. I drink bottled water but the reason I buy it bottled is because I like it fizzy. It's 27p per 2 litre bottle from Sainsburys and I drink about a litre a day. This is all a matter of preference, though. I'm happy with the purity of our tap water.