If you’re lucky, not very far.
If you’re unlucky, in some arid parts of the developing world, you could be spending hours walking several kilometres each day just to collect water to survive.
And forget about those romantic images of verdant oases. The water is often in polluted, dirty and in unsafe pools, especially for children.
However, putting the economics to one side for the moment, there are solutions. Cue the anaerobic digester and a new bit of technology attached to it called the McLanahan Nutrient Separation System.