Well most exterior paint is water base, unless somenoe uses oil base paints. Water base only has paint pigments in it and is harmless, (supposedly)!
But many painters when finished painting goes to the side of the house and uses the water spicket adn garden hose to wash their brushes, pans, and what nots.
I believe either way the EPA has overriding power of authority, but also, so does OSHA. But I think it depends on the circumstances at hand to decide which has authority.
Now as a former business owner, I would say as long as I am not putting harmful chemicals in the ground, they can just kiss where my place that is reserved for my ex-wife depends on who gets there first!!
The reason way back when the government mandated regulations to remove lead from paint products. The reasoning someone came up with water base paints and that is what primarily most painting contrctors use becsides easy clean up.
EPA AND OSHA can pretty much cause any business owner heartaches and financial hardships by not following the rules IF CAUGHT. But, you would have to prove the products you are using is not harmful as well, if EPA decides to cite you. One thing to keep in mind if you ever get cited and have to appear in court, (FOR ANY REASON, TICKETS, ETC) and you are POSITIVE you WILL WIN IN COURT. Make sure you tally up all your expenses for going to court, lost wages because you have to appear in court, etc. and have all your documents to prove such, Then as soon as you win in court, go to the county DA's office and file a compensation of your time, (bill), to be paid immediately, but you have to file it. I read cases where few people where sommoned to appear in court for tickets, fines, etc, PROVED their innocense and won in court, and they filed wage claims for having to appear and they ALL got paid what was submitted in court for their costs and lost wages. I know someone here in Texas who did such as I mentioned and got paid for his day of lost wages. The DA's office wasn't happy and niether was the judge, but because he won in court, the county had to pay him.
Many people DO NOT know this, and think they can't charge the courts for their time for having to appear. Fact is one can do it if they got their ducks in a row.