I got one from Aldi, I think. 2 litres of water. There is a part the you can put things like a pump, inner tube and all that in. It’s not huge, but its big enough. 2 straps, one around the waste and on at the chest. It’s a good lil bag! It only cost about £8 Or camelback Mule, any of them are good, Bit pricey though Matt!