Abstract: An automatic water shut-off circuit for a flushing toilet tank having a main tank replenishment valve, a main tank flushing or base valve, and a main tank float for operably controlling the flow of water through the main valve dependent upon the level of water in the tank comprising a secondary float operatively associated with the main float and a secondary water supply circuit operative to cause said secondary float to raise the main float in the tank in the presence of a leaking condition in the main flushing valve of the tank. The secondary supply circuit includes a branch conduit connected between the main replenishment valve and the secondary float, a two-position valve disposed in the branch conduit, and a third float responsive to said leaking condition to actuate said two-position valve to supply water through said branch conduit thereby to actuate said secondary float and turn off said main valve.