The SolarCat is completely self-contained unit. Once powered on, it is on a time to turn on and off in 6 hour intervals. (On for 25 seconds, Off for 6 Hours). As it turns on for 25 seconds, the SolarCat is priming itself to establish a siphon. In other words, if there is no water, nothing happens- yet, if there IS water, the 25 seconds priming will allow it enough time to entirely remove all of the water using just gravity. The SolarCat is clog-resistant (truly a set-it and forget it tool!), portable, has a built in timer to shut off at 32 degrees, wind-resistant (up to 70MPH), and removes ALL water down to 1/8.” To repeat that, it removes ALL water down to 1/8″. On a roof, the difference between a half an inch and an eighth of an inch can equal thousands of gallons and literally TONS of water.