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.

Step 1

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.

Step 2

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.

Step 3

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.

Step 4

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.