I have a small 3 bay self serve opportunity in a small town in Ohio. The owner says he has no records of income and just spends the money as it comes in! My question is, can I back into a gross revenue number by analyzing the water bill and total gallons used in a given month? My idea is to wash an average size car and time the length of time I used the spray wand. Then run the wand and measure the gallons used in that amount of time. Call this an average wash and divide it by the total gallons used in a month. Is this crazy? What holes are in my logic? Is there a better way to do this? Other thoughts. Each bay has credit card and coins. He obviously has access to credit card revenue. Can I estimate how much coin revenue there would be? Any help is appreciated!!