Why Is My Toilet Tank Slowly Losing Water?

Do you always hear a dripping sound inside toilet tank even when no one has flushed the toilet for a long time? Then, probably the tank’s losing water without flushing. But why exactly is your toilet tank losing water?

It could be due to many reasons, but the most common ones are- when there is something wrong with the supply line, the flapper has worn out or gotten stuck, the bolts are lost, or the washers have worn out, and when there is a crack in the toilet tank.

Whatever the reason is, in this very guide, we’ve discussed exactly how you can diagnose and solve these issues. So without any further ado, let’s jump right in.

5 Reasons Why Your Toilet Tank Might Be Losing Water

If your toilet is ghost flushing (A term used when the water inside the tank disappears without flushing), there are a dozen reasons for that. But in this very guide, we’ve shone a light on the most common ones. 

1. Loose or Cracked Supply Line 

Water flows into the tank through the supply line, and they are heavily constructed to last long. But as they age, due to high water pressure, some supply pipe gets cracked. And a cracked supply line is one of the most common reasons why toilet tanks leak

Apart from that, the toilet tank will also leak water slowly if the supply line connection to the toilet tank is loose. 

So how would you know if the fault is in the supply line? 

You might notice water on the floor around the toilet, and if you touch the supply line where it’s linked to the toilet tank, you might feel that water dripping out. 

If you feel the tank is leaking due to loose nuts, then simply tighten the nuts and put an empty bucket right under the nut so that if that leaks water, you would know. 

After a while, check on the bucket; if you see water in the bucket, even a little, the problem isn’t fixed yet. 

Remove the nuts and check on the nylon threads; if they have worn out, then that’s the reason why water drips out through the nut. Replace the nylon thread, and the tank shouldn’t leak water. When tightening the nuts, be gentle and don’t over-tighten them; otherwise, nylon thread will get damaged very easily. 

Plus, don’t forget to check the supply tube for leaks, and if you find any leak in the supply tube, then the entire line needs to be replaced. 

2. Worn out Flapper

Another very common reason why toilet tanks lose water is the worn-out or leaked flapper. In case you don’t know, the flapper is what stops the water flowing into the toilet bowl. 

When we press the button to flush, that lifts the flapper up by a little so that the tank can empty the water into the toilet bowl. After the tank is emptied, the flapper seats back into place, preventing water from flowing into the toilet bowl. 

Therefore, when the flapper has worn out, it won’t be able to stop the water flow to the toilet bowl completely; you might notice water trickling in the toilet bowl. 

The easiest way to make sure there is anything wrong with the flapper is to add some food coloring to the toilet tank water and leave it for half an hour or so. And make sure no one uses the toilet during that time. 

If you find the toilet bowl has water of the same color in the toilet tank, then definitely the flapper has worn out. In that case, you’ll have to replace the flapper

There are 2 types of flappers in toilet tanks; if the toilet flushes upon pulling a chain, that’s the traditional one, and if you’ve to press a button down to flush, that’s the modern one.

If you already know what flapper your toilet tank uses, you can buy one in advance. Otherwise, you’ll have to take the flapper to the store to bring the suitable one home. 

To replace the traditional flapper, you’ll have to:

  • Turn the water supply off in the tank and empty the tank by flushing it
  • Take off the tank lid, and you’ll see the flapper is secured with pegs on both sides
  • Unclip the flapper chain and then slowly free the flapper from the pegs, be gentle when removing the flapper
  • Gently put back the new flapper in place on the pegs. Ensure you have properly set the flapper; otherwise, it’ll come loose after a few flushes
  • Clip the flapper chain, and make sure to adjust the chain length so that anyone can flush conveniently
  • Once you’ve put everything back in place, turn on the water supply to the toilet tank and flush a couple of times to see if everything is working fine

To check if the flapper is leaking water, you can again put food coloring in the tank and then check after a while.

To replace a modern plunger or piston flush valve, you’ll have to:

  • Shut down the water supply to the tank and empty the toilet tank entirely
  • Remove the tank lead and locate the piston flush valve, which is tight in the middle of the tank
  • Hold the valve securely and gently turn it counter-clockwise; it’ll come off
  • Take the new one, place it exactly where the old valve was and then gently turn it clockwise to secure it properly
  • Turn the water supply on; as soon as water fills in the tank, flush the water to see if the new valve’s working or not

Check our step by step guide on Toilet Flush Valve Replacement HERE.

3. Stuck Flapper 

If the toilet flapper is stuck in an open position, it might not prevent water from flowing into the toilet bowl even after being in the best shape. So how to know if the toilet flapper is stuck? 

Check the flushing chain, handle, or button. If you notice that they’re not responding, then it’s due to a stuck flapper. To double-check, open the tank lid and see if the flapper is stuck by trying to push it down. If you can push it down, then it was stuck in an open position before.

After you have pushed it down, fill the tank with water. Then flush it down and check if the tank still allows the water to flow into the toilet bowl. If it does, there’s something wrong with the flapper or the piston flush valve. 

Have a professional take a look at the toilet tank to get rid of this problem. 

4. Leaking Bolts

If you find both the supply line and the flapper okay, then maybe it’s time to check on all the bolts and connections the toilet tank has. Usually, toilet tanks mainly have 2 bolts located at the bottom, which secures the toilet tank with the toilet bowl. 

Hold those bolts with your finger and check if they’re loose. Loose bolts will surely leak water. If you find them loose, tighten them and if you find them tight enough, unbolt them to check on the washers inside. The tank will lose water when the washers have worn out. 

Remove the washers and take a look; if they seem worn out, drop them and install new ones. To find out if the bolts are still leaking water, you can place empty buckets under them. If you see water in the bucket, then the bolts are leaking water. 

5. Cracked Leaked Toilet Tank 

If your toilet has a plastic tank, then there is a high chance that the tank itself is leaking water. Ceramic tanks also can have cracks. Inspect the entire tank thoroughly to find any cracks in it, and if you do find any cracks, the best option would be to replace the entire tank

You can repair cracked toilet tank, but that won’t do any good in the long run; it’ll start leaking again soon. So, it’s better to invest a few bucks and get a good quality toilet tank that will last for decades.

Installing toilet tanks is a little complex; you need to remove the bolts which are securing the tank to the toilet bowl. Then remove the water supply tube and things inside the tank, such as the fill valve, flapper, and flush valve. And then install all of them back again.

Therefore, if you don’t know how to replace a toilet tank, it’s better to hire a professional or have a friend or family member who knows how to do it.


So if you’re wondering why your toilet tank losing water, these might be the reasons. 

Like any other appliances, toilet tanks also need maintenance once in a while. For optimum functionality, they need to be checked and cleaned at least twice a year. 

Hello, I'm Jon C. Brown, an expert in the field of toilets. With over 15 years of experience in this industry, a significant portion of my life has been devoted to crafting high-quality toilets and bathrooms. Consequently, I've received countless inquiries about the toilet and bathroom industries. That's why, I've launched this website to provide top-notch solutions for all your toilet and bathroom related needs.

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