The number of gallons per hour that a misting system uses depends on the volume the system is spraying and the hours it has been on. Typically, the number of gallons used by a spray system can be calculated by the following formula: Number of gallons used = spray volume (gallons/minute) x working time (minutes/hour) The spray volume refers to the amount of liquid sprayed by the system per minute, and the working time refers to the operating time of the system per hour. These values can be adjusted according to the specific spray system setup.