well lets see, you have to actually drink alot of water a day if your active, about twelve 8 oz servings a day is around normal water consumpstion, that is 1 1/2 quarts. If your highly active expect to comsume twice that as your spending energy to fight for your life. However the game doesn't take into account how much water you drink from a source in a given click. but you can assume its like 8-16 oz of water if you want to rationalize the amount of clicks it takes to fill up your water gauge.
I do agree this game needs canteens. I suggest they can be crafted from leather making or maybe you can scavenge an old water bottle from junk heap. the containers themselves wont have much weight compared to the weight of the water inside them. water around weighs 1 fl oz per 1 solid once and given a 16 oz canteen should weigh then slight over 1 lb full. A small 16 oz canteen will give like two drinks. For devs It might be easier just to consider the canteens at always full water weight and not write code for the weight of an empty canteen and a full canteen.
tribes will need a portable water supply come longer battles and greater travel distances, while not a top priority it still is very important if we want to have some interesting seige warfare where it can come down to which tribe gather a large enough stock pile of supplies in case of hold out tatics where the attackers lack the force to destory walls but have a large enough army to prevent gathering.
I had an orange text in game saying that water containers are coming very soon (i asked for canteens) I do like the idea of being able to collect rain water. perhaps this could be an extension of woodworking or something