Photo of the type of bag to look for, you need to know the word for sack, and often a foreigner must push when asking. Generally in a foolish sort of way, the tourist and travelers just grab bottles, therefore vendors assume you want a bottle.
This bag was purchase in Ho, Ghana for 5 peso, about 3 Cents USA, and was freezing cold. I believe it is the custom to freeze the bags overnight here in Ghana.
It is very easy to drink, you bite the corner, a hole forms and you can squeeze the water into your mouth. What is nice, there is no air enter ling as it does when drinking from a bottle.