When you come into your bathroom, the last thing you want to be greeted with is the stench of sewer gases. But there they are, and when you look at your toilet, you see that the water level is low. Why?

The reason is either a blocked vent or a crack in the bowl. If there is a crack, you may need to replace your toilet. For a clogged vent, you will need to remove the clog from the vent opening on the roof.

Possible Causes

There are two reasons your water level may be dropping. There could be a crack in your toilet bowl, allowing the water to run out on your floor or down the drainpipe. Since it would typically be easy to tell if it is on the floor, it would probably be down the drainpipe.

Another reason can be a clogged drain vent. All of your drains link to the sewer, but they also link to a vent leading to the top of your house. When water flows down the drain, it often forms a seal causing low pressure behind it as gravity draws it down. This is what drives toilets to flush.

However, the vent system draws air in to fill the low-pressure areas in your drains. This prevents air from being drawn through your drains unnecessarily and possibly harmfully. 

A clogged vent means that when you drain water down a sink or tub, the water still needs to draw air. This air can be pulled through the drain into your toilet, potentially drawing water with it.

How to Determine the Cause

A hairline crack in the toilet bowl can be hard to see. But to see inside your vent at all, you would need to climb onto the roof.

So how do you decide on the problem? Luckily, there are two relatively easy steps to try and find out what the problem is.

  • Run your faucets. Make sure your toilet is full first. Then run your sink and tub faucet.
  • Listen for gurgling. If your drains are drawing air through your toilet, you should be able to hear gurgling as air passes through.
  • Decide what you heard. If you hear gurgling, then the vent is very likely at fault; if not, continue.
  • Turn all faucets off. You will need to avoid using water until you finish the test.
  1. Refill your toilet. Just make sure it is at its full level and mark its location.
  2. Wait a while. You should wait an hour or two.
  3. Look at the water level. If the water level is lowered with no other drains being used, then it is leaking through a small crack.

Toilet Bowl is Cracked

If your toilet bowl is cracked, unfortunately, it will need to be replaced. Luckily this is not that hard. Follow these steps.

  • Remove water from the tank and bowl. To do this, turn the water shutoff valve clockwise until it stops. Then, flush the toilet until the water stops. Sop up the remaining water from the tank and bowl with a sponge.
  • Remove the water line and tank. First, unscrew the water hose from the bottom of the tank. Then, remove the two or three nuts on the bottom of the inside of the tank holding it to the toilet bowl. Lift the tank off.
  • Remove the bowl. On either side of the toilet, there should be a nut holding the toilet to the ground; remove these. Now, lift the toilet up, cutting any caulk holding it down as necessary.
  • Install your new toilet. This will likely be a reverse of these steps. However, remember to replace the wax seal between the toilet and the flange on the ground. Otherwise, it may leak.

Clogged Vent

A clogged vent will require going to the roof of your home to clear obstructions from the vent itself. To do this, follow these steps. 

Open the vent. There are often caps or debris blocking looking into the opening of the vent. Remove these to clear the way.

Spray water down the vent. Use a garden hose and spray it directly down the opening. If it overflows, it did not clear the blockage, and you must continue to the next step. If it doesn’t overflow, congratulations, you are done!

Feed an auger into the vent. You will need a long one, 20 feet should do well. Feed it in and rotate clockwise when you hit a tough spot. This should help break up any stuck debris. Continue until the water drains.

Finish up and reassemble. Once the water has drained down, spray some more and see if it drains reasonably quickly. If so, put any caps back on, and you’re done. If not, repeat with the auger or call a plumber.

Water Level Set Too Low

You may need to adjust the water level because the water level may be set too low. To change the water level, use a screwdriver to adjust the valve on the intake pipe. Turn the adjustment screw located on the valve clockwise to increase the water level.

Alternative Causes

If you have any pets in the home, such as a dog or cat, they may be drinking from the toilet bowl. This could be causing a drop in the water level. You will need to be careful to lower the lid to prevent this, since the toilet may contain chemicals.

Another alternative is debris, such as tampons. These can get caught in the bend of your toilet, slowly siphoning water down the drainpipe. To solve this, use a toilet auger to clear the drain.

Related Questions

What is the Correct Water Level in the Toilet Bowl?

Many toilet tanks have a mark indicating the correct level of water for the tank. If your toilet does not mark the right level, you should make sure the water is about 1″ below the overflow tube.

What Determines the Water Level in the Toilet?

Generally, the height of the internal P-trap determines the toilet water level.. However, certain problems can interfere with this process. If the pipes are clogged, it may cause the toilet bowl water to be too high.

However, if the toilet bowl water is too low, there are several potential causes. You could have a cracked toilet bowl, a damaged fill tube, a blocked sewer vent, or a damaged fill valve.

Why is My Toilet Dry?

If your toilet is dry, it is not receiving water from the toilet tank. This could have a number of possible causes.

  • The water supply may be turned off. Check the shutoff valve located behind the toilet and make sure it is turned on. 
  • It may be a clogged intake valve. If this is the case, it will need to be repaired or replaced.
  • The toilet float may be stuck. Generally, gently moving the float and then putting it back in place should solve the problem.