If your toilet bowl water level is receding, there is damage to one of the components in the toilet itself. This is a common problem and it is an easy fix as long as you know how to solve it and what to look for. It concerns either the flapper valve inside the tank, the bowl ring or the intake on the toilet.
Flapper Valve Problems
When your toilet fills up after being flushed, the flapper valve allows water to drain into the tank. If the water level falls after the bowl fills up, this valve is probably the culprit. To check to see if this is the reason your tank is losing water, add a jar of food coloring to the back of the toilet tank. If the water flowing into the tank is colored, then you have a flapper valve issue and a new one must be installed.
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Replacing the Flapper Valve
To fix a leaking flapper valve, turn the water shut-off valve on the intake pipe just below the toilet tank to the closed position. Water will stop flowing into the tank. Flush the toilet and then remove the flapper valve. It is located inside the toilet tank at the bottom. The chain hook must be removed and a new flapper set into its place.
Adjusting the Water Level
The toilet water level may be set improperly if you continue to lose water. Every toilet is designed to be adjustable in terms of water levels. When the level is set too high or low the toilet will not function properly. To readjust the water level use a screwdriver to adjust the intake valve. Depending on your model, there is either a screw to adjust this valve on top of or at the bottom of the intake pipe inside the tank. Turn this to increase or decrease the water level.
Another possibility is a damaged seal inside the base of the toilet where it connects to the toilet flange (the pipe opening in the floor). When a toilet is rocked back and forth or jarred forward or backward, the water-tight seal (called a wax bowl ring) will pop open. Check around the base of the toilet for signs of water leaking onto the floor or seeping under the floorboards. This is a clue that the problem rests with the bowl ring. In order to repair this problem, the toilet must be removed from the flange and the wax bowl ring replaced.
A damaged toilet bowl is another problem that causes a water level drop inside your toilet. This is not very common but it does happen. Inspect the bowl and base of the toilet for cracks. Signs of water around the base of the toilet or water stains in the floors and walls are two clues this is the source of the problem. If replacing the bowl ring does not solve your issue, the toilet is probably cracked and the entire appliance needs to be replaced.