How much water do I really need?

Burningman.org recommends at least 1.5 gallons per day per person.  From our experience, that is fine just to survive.  However, if you crave that once in a while shower, you will need more.  Between showering, drinking and the swamp coolers, we go through about 5 gallons a day for two of us.  

http://burningman.org/event/preparation/playa-living/water/