The toilet's cistern is located in the tank above the toilet bowl. This is where water is stored prior to its travelling down into the bowl and flushing waste into the sewer line. When the cistern leaks, water is wasted as it runs into the bowl without the toilet being flushed. Adjusting the cistern to stop leaks is a straightforward job that can be carried out quickly and lowers monthly water bills.
Remove the toilet tank lid by hand, and carefully rest it on a flat surface; use caution, as the lids are quite heavy and will break if dropped.
Pour roughly a tablespoonful of vegetable dye into the water in the toilet tank. Wait half an hour and check the toilet bowl. If the dyed water has travelled into the toilet bowl, the cistern is leaking.
Push down on the float arm that the plastic ball is attached to. Notice that the when the ball is lowered, the inlet opens and water rushes into the tank. With older toilets, raise the level of the float arm and attached ball by bending the brass float arm downward. With newer toilets, use a screwdriver to turn the adjusting screw on the float arm clockwise to lower the ball's position. Continue turning the screw until the leak stops.
Replace the toilet tank lid.
Look on the inside back wall of the toilet tank for a marking that indicates the correct level of water in the tank. When the tank is full and the water level is at the mark, the float arm and attached ball should be in the proper position, and the water shouldn't leak into the bowl.