Since you are limited on your water usage you should look at using a rinseless wash product. You will not be able to get away with simply rinsing your car for the next 6 months unless you want your finish to be full of swirls and dull looking. The rinseless wash method can be completed fairly quickly once you've done it a few times. Check out the following video and product. I use it on my own vehicles and have no swirls in the finish.