An electronically controlled electro-mechanical device designed to limit a finite amount of water per flush to a tank reservoir of the common household toilet, or tank-less toilet or urinal, providing positive shutoff of water flow and anti-siphon backflow prevention. The toilet is flushed, the flush lever activates an attached tilt switch, the tilt switch actuates the countdown timer by means of electrical linkage, the countdown timer in turn activates the solenoid valve by means of electrical connection. The water enters the solenoid valve, passing through the valve and on to the float valve mounted to the toilet tank for fill up. The Countdown timer counts down from the full minutes and seconds set to 00:00 and shuts off the solenoid valve and ultimately the flow of water. The Countdown timer then resets itself to the time set in memory for the next flush operation. A float eliminator may be affixed to the toilet tank replacing the float valve, then connected to the solenoid valve. For the purpose of adjusting the volume of water per flush the Countdown timer can be programmed from 00:00 minutes and seconds to 99 minutes and 55 seconds. The average toilet will need approximately 2 minutes. It is suggested that the user flush and time his toilet prior to installation of the electro-mechanical solenoid valve unit and add five seconds to assure the proper volume of water per flush.