Water is a basic need, and dirty water kills lots of people every year. Luckily there are lots of ways to make water drinkable. No-Tech Magazine has a good review of OHorizon's open-source biosand filter plans. It is a relatively permanent solution, with a concrete case, yet only costs a few dollars each to make in quantity, as the form is made of wood. If you want the plans directly, go to OHorizons and fill out their form.