Click on the link to check the list of Airports.
Restrictions on taking liquids in hand luggage mean passengers often shell out for pricey bottles of water once in the departure lounge, or they may have to pay for expensive drinks on the plane, particularly on shorter journeys. But many airports have water fountains after security where you can fill up an empty water bottle or thermos flask for free - you just have to know where to find 'em.
Simply take an empty bottle with you through security - the Civil Aviation Authority confirms this IS allowed - and fill it up before getting on the plane. *The Department for Transport does not prohibit the carriage of empty water bottles through security in hand luggage.
Some may be put off that they are located in the toilets at Heathrow :D