How to Adjust Toilet Water Level. Adjusting the level of water in the toilet tank keeps your toilet flushing completely. The water level normally falls about 1 inch below the rim of the overflow tube. Lower levels don't allow the float ball to rise high enough to close the ball cock; a water level that is too high will continuously run, wasting water and forcing you to listen to the running water all day.
Bend float arm upward from the center to raise water level in a diaphragm ball cock and a traditional plunger-valve ball cock. Both of these types of toilet mechanisms have a large ball connected to the ball cock.
Bend float arm downward from the center to lower water level in a diaphragm ball cock and a traditional plunger-valve ball cock. Replacing your traditional plunger-valve ball cock with a newer diaphragm ball cock will eliminate many valve problems because it has a rubber diaphragm instead of washers and packing rings.
Pinch the clip on the side of the float cup and slide the clip up and down to adjust the water level in a floating-cup ball cock.
Turn the adjustment screw to lower and raise the water level on a floatless ball cock. Turn the screw counterclockwise to lower water level and clockwise to raise water level. Only adjust in 1/2 inch intervals at a time.