A low bowl usually means the bowl is not getting its refill water, or something is pulling water out. Check the refill tube in the tank, the tank water level, clogged rim holes, a partial clog in the trap, a blocked vent, or a cracked bowl. Start with the tank; it's the easy one.
What should you check in the tank first?
The bowl gets its refill water through a small refill tube. It runs from the fill valve in the tank to the overflow pipe, the tall open pipe in the middle of the tank. Every flush, the fill valve sends a little of the incoming water down that tube and through the overflow pipe into the bowl, while the rest refills the tank.
Fluidmaster, a toilet repair parts maker, describes it directly: the refill tube "delivers water directly to the toilet bowl with every flush." If that water never arrives, the bowl comes up short. So the first place to look is inside the tank. Take the lid off and set it somewhere safe. Then check three things.
Is the refill tube in the right spot? Fluidmaster says the tube should dispense water directly into the overflow pipe and sit on a clip above it. If the tube is shoved down inside the pipe, it can siphon water out of the tank and cause a ghost flush. If it has come loose or points away from the pipe, the bowl gets little or none. Clip it back so it drops water into the overflow pipe.
Is the tank water level right? Kohler's troubleshooting guide says to "confirm the waterline and water level match" and to adjust the level to the waterline mark in the tank if it's low. American Standard puts the target at about one-quarter to one-half inch below the top of the overflow tube. A tank that fills too low has less water to push through the bowl and refill it. Our guide on how to adjust a Fluidmaster fill valve shows how to raise the level.
Is the fill valve working? American Standard says a fill valve may be "clogged with debris and need to be flushed." On some models, the fill valve has a bowl refill adjustment that can be set too low. If the tank is slow to fill or the valve is noisy, see why a toilet tank won't fill. If cleaning doesn't help, the valve may need replacing.
Could clogged rim holes be the cause?
Yes. Water for the flush also comes out of small holes under the bowl rim, and mineral scale can plug them. Both Kohler and American Standard list clogged rim holes as a cause of a poor flush and low bowl water. American Standard suggests cleaning them with hot vinegar and a piece of wire. Kohler's guide says to clean the rim holes under the bowl rim.
Korky's slow-flush guide agrees that mineral buildup can clog the rim jets and weaken the flush, and it says to clean them with an in-bowl cleaner and brush or to carefully remove deposits with a wire. In Phoenix, this one is common. Phoenix water is hard, and lime scale builds up in small openings faster than most people expect. Our page on how hard Phoenix water is explains why. If the bowl looks stained under the rim or you can see white crust around the holes, start here.
To clean them, put on gloves, hold a small mirror under the rim so you can see the holes, and use a bent wire or small pick to open each one. Pour a cup of hot vinegar down the overflow pipe or along the rim and let it sit before you flush. Don't use bleach or drop-in tank tablets to do the job. Fluidmaster warns that bleach and chlorine products damage toilet parts.
Can a partial clog lower the water?
It can, and this is where a low bowl and a slow flush show up together. Korky's slow-flush guide adds that the height of the fill valve float sets the tank level, and a float set too low leaves too little water in the tank. Kohler's guide tells you to clear "any obstructions from the toilet bowl trapway or jet," then any obstruction in the waste line. For a clog in the trap, it says to use a plunger and a toilet auger.
A quick test: pour a bucket of water into the bowl fast. If it drains quickly, the trap is probably clear. If it rises and drains slowly, something is partly blocking the trap or the line. Try a flange plunger first, pulling rather than pushing. Then use a closet auger. Our guide on the difference between a toilet auger and a drain snake shows which one to use so you don't scratch the bowl.
Could a blocked vent or a cracked bowl be the cause?
If the trap is clear and the tank is fine, the vent pipe may be restricted. The vent is the pipe that runs up through your roof and lets air into the drain so water can move freely. Kohler's support page says that if nothing is blocking the trapway, or the problem continues after snaking, the vent pipe could be the culprit, and that with a restricted vent "you will not get a proper flush."
A blocked vent often shows up with more than the low bowl: gurgling sounds from drains, slow drains in more than one fixture, or a toilet that bubbles when another fixture runs. See why a toilet gurgles. Vent problems are usually not a DIY job, since the blockage is on the roof or in the wall.
### Can a cracked bowl cause low water?
Yes. If the tank level, refill tube, rim holes, trap and vent all check out, American Standard says the last possibility is a crack in the bowl. A crack in the porcelain lets water seep out slowly, so the bowl looks fine after a flush and then drops over the next few hours.
Look for a hairline crack, a damp spot on the floor, or water that keeps disappearing overnight. American Standard's fix for a cracked bowl is to replace it. Our page on what it takes to replace a toilet explains what goes into the job.
If the floor around the base is wet, the problem may be the seal instead. See why a toilet leaks at the base.
### When should you call a plumber?
Call one if the tank and rim checks don't help, the bowl stays low after you clear the trap, other drains gurgle or back up, or you suspect a crack. A low bowl paired with a sewer smell is worth checking soon, since the water in the bowl is part of what keeps sewer air out.
HQ Plumbing and Air can find the cause, whether it's a clog, a vent or a bowl that needs replacing. We give you the price up front, before we start.