Personally I don't wash them, unless there's something unpleasant or likely to mark them same with my windsurf sails, rolled and stored from riding in salt water, salt is a preservative, less likely to get mice and furry things making nests and having a chew. Kites however don't get left that long these days, but salt accumulation just wrapped in the bags aint really an issue, leaving them flapping on the beach for one hour will do more damage.
If you do wash them in fresh water then make sure they're totally dry before storing, if say it's at the end of the season and they're losing their water repellant quality (water doesn't 'pearl' when applied) then use a reproofing spray (google is your friend here, round here some form of scotch guard or sail company stuff).
Now that's the kite, the bar and lines completely opposite, always wash the bar, pay especial attention to any stainless or metal bits, alooominum (for our colonial cousins) doesn't like salt water and will degrade especially if in contact with stainless and the alleged stainless that our far eastern scalping manufacturers use is as much use as a chocolate fireguard. So every time especially if on a sandy beach.
Of course to be really safe you should use distilled water..