The fresh water and the gray water tanks hold 9 gallons each. That’s plenty of water for several days of cooking and cleaning up afterward. The vans come with a hose attachment you can use to refill the water whenever you need it. It will attach to any standard spigot.
Make sure you empty the gray water before you refill the fresh water! If you’ve used the full 9 gallons of water, you likely have about 9 gallons of gray water. It will back up into the sink if it overfills, so make sure you empty it before that happens!