http://www.glastonburyfestivals.co.uk/news/help-us-reduce-the-number-of-plastic-bottles-at-glastonbury

Hmmm. We've always taken and kept 750ml water sports bottles, filling them from the tap when the rum ran out. What has been annoying was the policy at some of the bars to refuse to give you the cap to bottles of things like Coke so you could re-use them as water bottles. Perhaps they should fix that rather than trying to sell us a steel bottle.