If your Sippy bottle doesn't work out, we have one of these bottles..
http://www.petsathome.com/shop/large-chew-proof-water-bottle-by-super-pet-15861
The 'nozzle' end sits in a kind of cradle which is held onto the bars with two hooks. The main body of the bottle is held in place with a clip which is kinda like a spring with a clip on either end. (A bit like a bungee)
The spring fits into a notch in the bottle so it doesn't slide around. The bottle has a flat back so it sits flush to the inside of the cage too. As it's glass/metal it's completely chew proof
(I hope that make sense - it's kinda hard to describe!)
Oh and there's a cute mini rubber duck which shows easily how much water is left! xx>>>