B.J.
The cities in the North Texas area all follow the EPA's Phase II regulations and Best Management Practices(BMPs). You can find them by doing a websearch for EPA.
It is also a good idea to check with each city's Storm Water Management Department before working in their city. Most have their own BMP's and may also have local codes or restrictions that pertain to pressure washing.
Here is a website that has a lot of usefull info about Storm Water Management in North Texas.
http://www.dfwstormwater.com/
Check with each city's Waste Water Management (sanitary sewer) office if you plan to capture wash water and pump it into the sanitary sewer. They may have restrictions on certian chemicals or on the volume of water entering the sanitary sewer. If you will be capturing your wash water and haulung it somewhere else to be disposed of(for example: a liquid waste disposal facility), you may be required to have a permit to transport waste.
As for licensing and permits, So far I have checked with 4 different cities in the Dallas area and haven't found a city, yet, that requires a license or a permit to pressure wash. That doesn't mean there aren't any. Check with each city you'll be doing business in. Be specific with your questions. One city I checked with told me that I didn't need a licence or permit to pressure wash but, if I was doing it as paint prep and I was also doing the painting(may also apply to deck sealing) I would need a building permit to paint.
Hope this helps,
Good Luck