If you are referring to the bowl water level, that is controlled by the small refill tube from the valve to the overflow pipe. If is is obstructed or not flowing the proper amount of water, the bowl will not refill properly. Sometimes, because of high water pressure, the tank will refill too quickly to allow the bowl to refill to the proper level, and shutting the wall stop a little may correct it.: When the bowl refills, the level is much lower than normal. How do I fix this?