Unlimited
The WaterMill is powered by a 12 volt direct current pump that consumes less than 35 watts of energy. The power source can be any 12 volt battery (car or motorcycle) that has a capacity or 7 Amp hrs or greater (deep cycle is preferred). The battery is rechargeable using a simple 20-watt solar panel. Thus with a few additional items, you essentially have an infinite supply of potable water in emergency situations as long as there is a source of surface water (pond, lake, stream, ditch, rain, etc) and sun.