I always recommend to not worry about washing your solar panels. In southwest Colorado we get enough rain and snow to clean the panels. Also, if your tap water has minerals in it (which I think it all does in this area) you can get water spots and mineral deposits on the panels. A study done by the University of California at San Diego has shown that even if it hasn't rained for 145 days, in dusty southern California, it only reduces the output of your solar panels by 7.4% or about $20 for a 5 kW system. Probably not worth the effort or expense of cleaning your panels.
Durango Solar - FAQs
Frequently asked questions about solar photovoltaic systems in Durango and their answers.