This week Caroline Quentin and the team are in West Sussex at the Nutbourne Pumping Station - and it is a wreck. It closed in the 1970s and is now an industrial-sized bunker full of rusting, redundant, heavy duty machinery. But this ruin was at the heart of a revolution that saved our grandparents' generation and changed society forever. It tells the story of the water we drink, and not that long ago drinking British water could literally kill you.