Well, you really can overthink these things...When my husband first told me he wanted us to get into this business, I was decidedly lukewarm about it until I hit upon the environmental angle ( I really am a treehugger at heart). That's one of the only things I miss about living in the Puget Sound-the environmental awareness, recycling, etc. We have the same laws here as everybody else does, just not much in the way of enforcement. It pretty much boils down to you have to control your watewater IF
1) You are cleaning any surface that has any contaminant that should not get into the groundwater-mostly would be grease, oil, fuel, and 2)you are working on an impervious surface. The EPA is well aware of the filtering properties of soil, and remember- "the solution to pollution is dilution". makes my treehugging skin crawl, but it is true-enough water will cure a lot of environmental evils. If you wash houses or buildings that have grass or gravel around them, and you aren't using any really nasty chems, you'll be OK. What you can NEVER do is let water run into the storm drains. You block the drains, contain the water, vac it up, filter it, and arrange to discharge it in the municipal sanitary sewer. Do some reading up on BMPs (best mangement practices) for your expected worksites. Basically, they just want to know that you're aware of the issues and you're trying. My homemade containment dams don't stop 100% of the water, but they do stop probably 95% of it, and the municipalities are OK with it, because they see that I'm trying, and I do have an agressive pickup and filtration/treatment system in operation.
I was where you are not too long ago-confused about everything but my desire to do it right. Hopefully in your part of the country you have more people with answers, and less who look at you like you're nuts for wanting to do it the ethical way and not the easy way. Idaho's a little backwards still...