Just found this in Tesco. A Brita fill and go water filter bottle. Don't get me wrong, £2.50 is a lot of money for a water bottle when you can buy one with the water already in for about 50p but if you're that way inclined then £15.00 down to £2.50 is a steal.
This was in the Harlow Edinburgh Way store and there were quite a few. Not sure if store specific. Random but only the blue was in sale, other colours were full price.