I saw a fellow camping near me do this last year so I've started doing the same thing. I got a water bladder (
https://www.amazon.com/gp/product/B009ONFDEM) and pump (
https://www.amazon.com/gp/product/B00P8BE6S8) from Amazon, plus a 25' length of water hose, a "tank filler" attachment (
https://www.amazon.com/gp/product/B0006IX850) and a good length of 16ga wire and some quick-connect fittings. I put a quick connect fitting in my forward storage bay connected to my battery with a fuse.
I travel empty as others noted above. When I get set up, I go to my potable supply source and fill the bladder. The bladder has two garden-hose fittings, one male and one female, so a short length of standard water hose does the job here. If you're at a campground that mangles the threads to prevent people from permanently attaching hoses, a Water Bandit (
https://www.amazon.com/Camco-Connects-Standard-Various-Sources/dp/B000EDOSKG) is a nice accessory to have handy. The bag stays in the bed of my truck and I got the 60 gallon one (way more than I needed, I should have gotten the 30).
When I get back to the camp site I connect the bladder through the pump to my hose-filler port on the camper. The listing on the pump isn't super clear about this but it does come with barbed fittings exactly the right size for a standard garden hose if you cut it in half. it does not include hose clamps. They aren't really needed, this is all low pressure, but I added them anyway just to keep everything tight. Go gently, the fittings are plastic.
This is a fast process. It only takes about 5 minutes to fill the bladder and 5-7 more to fill the camper from it using the pump. With this setup, a similar one for waste water (with a Clean Dump macerator pump and Camco waste tank), and my solar setup, I can camp anywhere more or less indefinitely, and always travel with empty tanks.