No... we use tap water. The tank I refer to is our "buffer tank" on our trailer. I HAVE to use a tank even though we use customers water source. The "Buffer tank" is needed due to flow variations from the water source. Our machine has an 8 gpm pump. The source may not be providing sufficient flow to feed our pump. This can cause a cavitation and damage the pump. So we receive water from the source into a "buffer tank" and then draw from the tank. If the original source is flowing perhaps 7 gpm (-1gpm deficit) and we already have 100 gallons of "buffer", we will get 100 minutes of constant run time before having to stop and let the source catch up. Since, normally, we don't have constant open trigger, we usually can continue work without interuption. However, if the source is flowing say 10 gpm, the tank will overflow with excess. We have a float valve in the tank to shut off the source so water is not wasted.