I'm with Teacher on this one.

In my BOV I have a case of bottled water that I rotate. In my BOB I only carry 2 one liter soda bottles of water. I treat with Aqua Mira when backpacking and in an EOTWAWKI event I would use Chlorine bleach to treat as I go.

Lightweight backpackers seldom carry more than 2 liters of water at a time.