UK Heatwave: Where does London's water supply come from?

With London in an extended period of dry weather, Thames Water recently announced a hosepipe ban in its coverage area to come into effect within weeks.

All water companies are monitoring usage, storage and rain very closely and the picture could change quickly - all of them are asking customers to use water responsibly.

BBC London's environment correspondent Tom Edwards explains where London gets its water from and what needs to be done in future to safeguard supplies.