There is no difference except the £1.00 you loose.

Drinking tap water H2O is the same as the bottled variety H2O. The main diffence being the money you save enough for an extra holiday every year of your life. 

http://www.thisisnottingham.co.uk/like-bottled-tap-water-differences/story-19001646-detail/story.html#axzz2bDBUUyNz