Allen
Sorry, you hit a raw nerve with most of us. From the tone of your post, you gave us the impression that you did not, in fact, know anything about washing cars.
Did you lose the thread where you asked this question last month? "need help asap. Can cars be cleaned with a normal power washing unit or do they have to be cleaned with the hot units or with a dio0onized unit? I need to know yesterday. I have a bid that I am considering with a lot with one thousand cars on it."
or the awesome response from John Montag? "My advice is to RUN!!! Now that I got that outta' my system........ The ultimate set up would be an RO system, but is very costly and hard to justify for what you're going to get paid per car. In cooler weather (MI) you might be tempted to use hot water. However, the quick change in surface temperature on the metal and glass only helps to calcify the hard water, leaving deep water spots that are extremely difficult to remove.
We use to do between 2,500 & 3,000 cars weekly for dealers. If I remember correctly, we used roughly 6 - 7 gals. of water per car. Keep this in mind if you're going to use a portable tank. We ALWAYS used the dealerships outside water source, so this wasn't a big issue. The drawback to this is that you end up using 200' - 300' of supply hose to the machine, and another 200'+ of pressure hose. That's really hard on the machines. Not to mention that your supply hose gets run over a lot, or parked on, interrupting your water flow. Plus, using the dealership's water, you're at the mercy of the supply's water hardness.
Our crews consisted of 3 guys. One sprayer & two chamois dryers. Our average was 50 - 55 cars per hour, doing exceptional work. You can do more per hour if you're sloppier. We started at daybreak 5 - 6 a.m. Firstly to avoid the heat on the cars and heatstroke. Also to avoid a lot of customer traffic while spraying. Most dealerships are going to want you to do this work on Thursday or Friday so the cars are "standing tall" for the weekend traffic. This means you have a small window of opportunity. If there's any rain in the forecast, we litterally were calling our crews at 11 p.m. to tell them wether we were working the next day or not. Don't be surprised when the GM of the dealership calls you at 9 p.m. to say "it looks like rain, forget the wash this week!" Somehow these guys believe rain cleans cars as good as pressure washing.
Used cars: The sprayer has to be very careful about loose paint, pin striping, loose moulding, etc. I've watched them peel off pin stripes in a second, or remove a giant sheet of poorly touched up paint areas. And yes, dragging the hoses over the fenders will scratch the hell out of them. If you're gonna' do this, invest in non-marking hose for the section at the gun.
The long & short - Yes, you can make money if you do it right, but there are a lot of variables. I didn't even get into employee problems. The average price around here was $1.35 per car. We paid our crews by the car, not the hour.
Good Luck with all that!