Howdy, the gallon a day rule has served me well for a good while. For two people overnight I'd say two frozen gallons and two regular. Like was already said above, you can use river water for dishes and such. Most microorganisms that you have to worry about won't survive being boiled and dried overnight on whatever dishes you wash. Just a thought, you can use a steel coffee pot like you find in camping stores to boil extra drinking / cooking water. If you filter the water thru a hankercheif before adding it to the pot to take care of the bigger debris and then boil the heck out of it you should be ok. Hope this helps, have a good time man.