Busby's Stream is the only source of water available to the ICM, dividing their territory from the Friends of Man's. (It is rumoured that there is a series of ponds and streams inside the caves themselves. However this is not yet proven, as nobody will look for them - they'd rather walk for ten minutes and live a relatively long life than get lost in the caves looking for something that probably doesn't exist)
The stream is not very wide, and not very deep, but it's clear and fresh, with the sweetest water you'll ever taste.