I certainly hope you have a few gallons tucked away. How far are you from an open source like Rock Creek or the Potomac itself?

The best and highest use for water is drinking. Water used for other purposes can be recycled - save your bath water (you can get clean with a surprisingly small amount)and use that for flushing. The water content of some foods, especially fruits, is surprisingly high and quite useful in an emergency.

As supplies get tight, the only use for water will be drinking....