In reply to GLUF:
I got one of these, which for £20 odd is excellent value.
www.watertogo.eu
If you want to have more than 750ml, then take another (any) bottle with you, fill them both up, drink out of the water to go bottle, and then fill that up from your other one. Don't do what I did, and try to squirt water but of your water to go bottle - the over pressure isn't good for it!
I used it wild camping in the Ecrin and loved the lack of waiting, nasty taste and hassle. I like being able to just top up whenever you find a stream.