I can't vouch for Heathrow specifically (sorry) but I flew from Manchester on Friday and the vast majority of the stores airside had large signs posted stating "All items purchased in this store can be taken aboard flights, including liquids and gels, with the exception of flights to the USA" or some such.
According to the BAA and the Heathrow website:
Further passenger information
Before security: All shops and catering outlets are open to all passengers, but any liquids and gels purchased must be packed into your luggage for check-in. Any other purchases must fit into your ONE item of hand baggage.
Once through security: All shops and catering outlets are open to all passengers. If you are travelling to any destination except the USA then you can take all items purchased in the departures lounge into the aircraft cabin.
If you are travelling to the USA: Extra restrictions are in place. Passengers will be subjected to secondary security searches at the gate. No liquids purchased in the departure lounge will be allowed into the aircraft cabin and any drinks or liquid items must be consumed before boarding. Food, however, is allowed. Passengers boarding flights to the USA and items they are carrying, including those acquired after the central screening point, will be subjected to secondary search at the gate and any liquids discovered will be removed.
So if you're traveling to the US, as I was, you're still pretty much SOL, but all other destinations allow water and other liquids. (FWIW, I was allowed to carry on a contacts case filled with solution for my contacts when flying to the US on 22 September, but not my 2oz bottle of saline solution that I was allowed to carry on when I flew from the US to the UK on 16 September.)