Ortlieb says about the Water Sack
Water bag with wide neck closure: flow-control valve with dust cap: roll closure with hanging option: large opening for scooping up water: compatible with hand and gravity water filtration systems. Not suitable for water transport in the horizontal position. Please note: Dimensions given are of the bag's height with the roll closure closed (3-4 times rolled up). For the opened height, add approx.15-20 cm!
Accessories available separately: shower valve.