A bag for carrying water?

So the last 18 months or so I’ve weaned myself off carrying gallons of water around and can get by with 250-500 ml on most rides

A conventional bottle takes up too much room and half-filled reservoirs are too much faff with clips and tubes and valves and all that crap. What I want is a flexible (flat?) bottle that fits inside a backpack that can be compressed as it empties. Like a bag with a drinks cap on it.

Any ideas? Something from the world of running maybe?

Ta

Platypus

http://www.cascadedesigns.com/platypus/bottles-and-storage/category

A lot of camping shops stock them or widely available online.

Can get them anywhere, really cheap.

Edit: wish I’d found this one before posting the link. Or this one.

nice one thanks fellas

Be warned, the cheap ones tend to have leaky valves and are prone to splitting…

Platypus is good, I like mine but… Surely more faff than a camelbak? Pretty much the same amount of faff to prepare, and then much more every time you want a drink. I fannied around with alternatives but returned to the camelbak.