I was thinking this would be useful for restoring stamina/a basic nescessity. It could be used 10 times before having to fill it up at a lake or well.
A water level could go either where happiness is, or the karma depending on what they take out.
I'd suggest, say 6 bubbles that slowly empty as you walk.
Being in desert would increase this.
One drink could restore 5 stamina, but you cant drink more than the 6 bubbles full of water.