We also use the water for consumption. I sanitize it several times a year with bleach, followed by white vinegar and baking soda. Takes about 30 minutes and all is clean. Been doing this for over 10 years with no problems.
Generally, we will put 4-5 gallons in the tank from home when we start a trip. this will get us where we are going and good for the first night if necessary. We carry a full 5 gallon container in the truck for emergencies and also use it to refill the tank . Once we get to the site, we will fill the tank from the local source. 30 gallons will last us for at least a week, usually longer. We try to be very conservative with water. We usually catch most of the gray water in a 2 gallon tub that sits in the sink. We put most of the gray water into the toilet as the black tank is usually the last to fill.
Vann