Welcome aboard....very common problem. I have family in SE Arizona, and they suffer through the same thing. The elegant solution (as mentioned above), especially for "full" hose-driven washes, would be to tap in behind a water softener. (A DI kit is also very effective, but much more expensive.)
The third option, and honestly I think it's the best/easiest/cheapest, is to use a No-Rinse wash system. I love Optimum NRWS, and for this purpose it's very hard to beat. I recommend using a bit more of the product than directed, and obviously if possible, use softened water in the buckets.
Beyond that, if you can be fairly diligent about applying a good quality sealant as your last step (I'd recommend Blackfire WD/Four Star UPP as ideal solutions) you'll have a great line of defense. Wolfgang DGPS is another favorite, although IME it's not quite as durable as the others. However, it looks GREAT, especially on dark colors. If you go that route, perhaps consider upping the frequency in application. Good luck...
