What is the average monthly water bill for a car wash that draws its
water from a municipal source?

Hi, 

Here is a PDF file which is Titled "Water In the Car Wash" from the
American Carwash Industry, which tells all about water usage, how to
cut down on it, and where it is used.

http://www.p2pays.org/ref/22/21070.pdf

I found this on the Industrial Water Conservation website at
http://www.p2pays.org/water/industry.htm

Google Search 
+"Water Usage" +"Car Wash"

thanks, 

webadept-ga

OK. We have the links to the PDf files but how about posting the
answer to the question here?

Here ya go... Some stats for you. 

GPV = Gallon-per-vehicle

Without a reclaim system
Low end: 15 GPV for self-service car wash
Hign end: 85.3 GPV for frictionless conveyor car wash

With a reclaim system
Low end: 8 GPV for self-service car wash
Hign end: 31.8 GPV for frictionless conveyor car wash

Now takes these numbers, call the water company in your area you plan
to have this and ask them the cost per gallon on water. Then you will
have your cost. I would do this for you, but you didn't give a city.
These numbers are just an idea for you, your usage would be a little
more or less depending on how dirty the car is and where the car wash
is located.