For our minivan camper conversion you shouldn’t have to worry about water tanks like normal RV’s have, where they are mounted and piped. Water containers that we would use in our minivan are the portable type. How much you need depends on how you use it and where you go with it. For typical day to day traveling, you won’t need much. You should already have at least three gallons in the portable sink. The porta-potty tank should be all set with about three gallons of it’s own. So that only leaves what you need for drinking and cooking. Usually about 5 gallons should be more than enough, and some of that can be bottled water.
Water containers come in all kinds of styles, but one thing they have in common.. they are all white blue or clear. They can be anything from quart size to five gallons or more. Some are solid containers, and some are collapsible containers. It is up to you as to what kind works best for you. They are available at most RV and camping stores, and some hardware stores.