try washing with optimum no rinse instead of a hose wash. You'll unfortunately need to go down to wal-mart and get some of that cheap water they sell to you where you fill up your own container. I guess you'll need to be a little more economical with the amount of water you use. Generally two ounces of No Rinse solutions is used with one gallon of water. That's plenty to wiped down the car.
as far as rain, that could be tricky but I recommend the following:
after claying the car use an acrylic paste wax. I use FK1 1000P. It dries like cement. I use at least two coats for max coverage. Once it dries use a polymer spray like
FK1 #425 frequently. It provides a very slippery surface that might be tricky for droplets to bond to.
here's another Optimum product
LINK
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