I carry around 1/3 full in the fresh water tank, and fill up at the campground. Many of the campground general use faucets do not have threads. If you want to fill your tank from them is is handy to carry a "Water Thief
". I modified mine with a pair of hose clamps - a long hose will sometimes create enough back pressure to pop the brass fitting from the device & the rubber end from the faucet.
If you use 5 gallon buckets to fill your tank, be sure to try before you leave home to make sure you have a way to get from the bucket to the trailer...