For 4-5 days: Fill the water at your previous stop then if you conserve you can go the 4-5 days without having to refill. When you leave, your park might have a dump station. If not, here's some help:
http://www.rvdumps.com/Some help with conserving:
Don't let the water run when washing hands; showering; brushing teeth
Take paper plates and you don't have to do dishes at every meal and perhaps not even every day.
Do dishes in a dishpan and use that water for flushing the toilet.
Grill outdoors
Showers: Catch the water in a jug when trying to regulate the water temperature. It's clean water so use it for dishes, etc. Do a quick wet down. Turn off water. Soap up. Do a quick rinse. It's amazing how little water you'll need.
Good luck. You can do it!!