I have a 65 Gallon tank. Most of the time I only fill it half full. This gives me enough water to fully detail about 3 cars. The full tank gives me enough to detail 6 to 8 cars. Now I only use the water with a electric 1.2 gpm presser washer to wash the wheels and wheel wells of cars and tucks. I also use it to wash floor mats too. On most cars this does not require much water. I live in an area where there is a lot of farm and off road driving and mud. So for some SUVs this requires a bit of water. I do wash the rest of the car with ONR. I also use the presser washer to wash off the bugs on the front of a car it just makes it faster than tackling it with only ONR.