Toilet Bowl with very little water

Why Does Toilet Bowl Keep Losing Water?

It’s the middle of the night and you have to go to the bathroom. You get up, turn on the light, and walk into the bathroom. You sit down on the toilet seat… and then you realize that there’s no water in the bowl! What do you do now? Has that happened before as well?

What do you think, why does the tank lose water? The two primary reasons why a toilet gradually loses water are clogged air vent, and cracks/leaks in the toilet bowl. Apart from that, if the water level is low soon after you flush that indicates a problem in any of the tank’s components, i.e. flapper, or the refill tube.

In this comprehensive guide, we will answer your question and provide solutions for why your toilet bowl keeps losing water. Let’s get started.

Causes of Drop in Water Level

Generally, a toilet bowl loses water when the air vent is blocked, or when your toilet bowl or toilet itself has cracks.

a clogged air vent
Image from Fiedler Your Pumping Specialists

Cause #1 Clogged Air Vent

A clogged air vent may cause the water level inside the toilet bowl to drop gradually.

Underneath the toilet, you have a wastewater line, which is linked to an air vent that goes to the roof of the house. The air vent is like the breathing system for the toilet and helps to keep the sewer gases from coming into your home.

When the vent opening is closed, either due to debris, some bird’s nest, or leaves. Then, wastewater running in the sewer line that would have sucked air from the vent, now sucks off water from the bowl, dropping its level. Additionally, the gases will build up in the sewer line and eventually come up into your home through the toilet. So, one of the signs of a clogged vent is a bad smell.

cracked toilet bowl
Image from Coleman Plumbing Maintenance & Repair

Cause #2 Cracks in the Toilet Bowl

Another reason for the gradual drop in the water level of the toilet bowl is hairline cracks. If there are cracks in the toilet bowl, then water will slowly leak out of these cracks.

These cracks may be anywhere in the toilet :

  • The porcelain on the inside of the toilet bowl might have hairline cracks
  • A crack might be in the flange (the part of the toilet that connects to the sewer line)

All of these cracks will allow water to slowly leak out, which will cause the water level inside the toilet bowl to drop.

plumber fixing a toilet tank

Cause #3 Issues with the Tank Components (Flapper, Refill Tube)

Sometimes you notice a drop in water level soon after you flush. If that is the case with your toilet, then this indicates a problem with one of the components inside the tank. The two most likely culprits are the flapper and refill tube.

The flapper is a rubber guard that covers the opening between the tank and the bowl. When the toilet is flushed, the flapper lifts up and allows water to flow from the tank into the bowl. If the flapper is not sealing properly, then water will leak out of the tank and into the bowl. And when you flush, a very less amount of water will be drained into the tank. Or sometimes, the chain is too loose that the flapper doesn’t lift properly, and the whole water isn’t sent to the bowl. This appears as the water level in the bowl has dropped.

Another flaw might be in the refill tube. The refill tube is a small tube that runs from the fill valve (the part of the tank that fills up with water) to the overflow tube (the pipe that drains excess water from the tank). If this tube is not positioned properly. Then, the tank doesn’t fill up properly and significantly flushes less amount of water in the tank.

Locating the cause of the Dropping Water Level

If you don’t witness any signs of leaks around the toilet and are not sure about the cause of the drop in water level. Then, you can follow these steps in order to find out the real culprit.

#1 Check the water level in the tank

Firstly, open the tank and see if the water is filled to the marked line. If not, then first you need to fix the fill tube and ensure water reaches the marked level. 

a flushing toilet

#2 Flush the toilet

If the toilet tank is full, and everything inside the tank seems fine. Flush the toilet. Does the whole water move into the bowl? If not, check the tank’s seal and fix it.

#3 Pay attention to gurgling sounds

Once you clear the initial two steps, the toilet seems fine there. Then, pay attention to the gurgling sounds when the water flows. You might notice a bad smell and gurgling sound if the vent is blocked.

#4 Clean the floor around the toilet

So, if you hear no sounds at all, then it’s time to look for the leaks around the toilet. Clean the floor around the toilet. You may use a cloth or towel to fully dry the area.

the toilet has a leak

#5 Look for leaks

Wait a few minutes, does any area of the floor get wet? If so, that means the toilet bowl is leaking from somewhere. If the leak is near the flange, you can fix it by replacing the flange. Else, you would need to replace the whole toilet.

How you can fix Toilet that a loses Water

Now, that you identified what might be the issue with your toilet. Let’s see what can be done to fix the issue in each case.

Fix # 1 Unclog the Air Vent

If the cause is a clogged air vent, then you will need to unclog the vent. To appropriately do so, follow the mentioned steps.

  1. Get to the roof or the place where the vent’s opening is located. Also, take a garden house and toilet auger with you.
  2. Remove any leaves, nests, or anything blocking the vent’s mouth.
  3. Pour water into the vent with the garden house. You might notice it drains slowly.
  4. Push the auger in and force the debris through the pipe.
  5. Keep pouring water until the whole debris gets removed.
replacing the toilet, tightening bolts with the nuts

Fix #2 Replace the toilet

If the cause is cracks/leaks in the toilet bowl, then you will need to replace the tank.

Some plumbers may recommend you use a silicone sealant or any adhesive for covering the leaks. But that is usually not favorable. It is in your best interest to replace the whole toilet. It would seem a difficult task for you, so you can take professional help.

However, if you want to do it yourself, follow these simple steps.

  • Turn off the water supply valve and remove its connection from the toilet
  • Flush the toilet.
  • Take off the tank’s lid and remove any remaining water using a towel.
  • Using the same method, sponge out water from the toilet bowl (Wear Gloves while doing so).
  • On both sides at the base, you will notice bolts; remove them using a wrench.
  • Carefully grab the toilet using both hands and put it aside.
  • Examine the toilet flange and gasket, if they are cracked or damaged you can easily replace them now.
  • Place a new toilet on the flange.
  • Place the bolts and reconnect the water supply line.
new flapper installed
Image from Pride Mechanical

Fix # 3 Fix the bad flapper

If the cause is a water level that is low soon after the flush, then you will need to check the flapper and fill tube.

Sometimes, the flapper doesn’t lift properly, and as a result, less amount of water is sent to the bowl. It seems like the water level has dropped. So, you can check if the flapper chain is loose. If it is, tighten it. Sometimes, the flapper doesn’t seal properly. In that case, you might need to replace it.

To replace a bad flapper, follow these steps.

  1. First cut off the water supply to the toilet. For that, turn the shut-off valve clockwise.
  2. Remove the tank’s lid, and flush the tank.
  3. For removing some excess water at the tank’s bottom, you can use a sponge or cloth.
  4. Locate the flapper. It sits at the bottom of the tank.
  5. Unclip it, and remove it from the nearby components carefully.
  6. Place the new flapper in its place, clip it and attach it to the nearby components
  7. Cover the tank with its lid.
  8. Turn the shut-off valve clockwise.

Moreover, at times when the water level is not at the desired height, you can adjust the float ball attached to the fill tube.

Final Words

With a little bit of effort, you can keep your toilet bowl from losing water and ensure that it stays clean and functioning properly. We hope that this guide has helped troubleshoot the issue of a toilet losing water.

If you are still having problems with your toilet bowl losing water, then it’s time to call a professional. A plumber will be able to diagnose the problem and fix it quickly.

Do you have any additional tips for keeping a toilet bowl from losing water? Share them in the comments below!

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One Comment

  1. Hi Anthony
    Our house is eight years old. We have three toilets. All three have been loosing water from the bowl for the past month. The tank is full when you flush the toilet and fills up then shortly after starts loosing water. You can actually see it going down. It settles about an inch from the original fill but over time will loose more water.
    We have had two plumbers out and they can’t find the issue. The roof vent is not clogged, the toilet bowls don’t have cracks and no water on floor. We had a slow draining tub so we cleared that and it’s running good but still have the dropping water problem.
    Components in tank are all good.
    I even called the city to see if they did any work on the sewer that would cause this snd they haven’t.
    We have a sewer pump and it seems to be working well. I even called the sewer pump company and asked if it could cause the levels to drop if not working proper. Answer was no, it would just keep running or not empty.
    We are at our wits end trying to figure this out. Any info would be appreciated c

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