The main causes of a slow water level drop in the toilet tank are a cracked tank, a faulty flush valve system, a faulty fill valve shank washer and/or locknut, and a malfunctioning flapper valve.
It’s happened to all of us. You go to the bathroom, do your business, and flush – only to see that the flushed water is not sufficient to clear the waste out of sight.
You flush again, and again, but the water level in the tank doesn’t seem to be rising.
When you have a closer look at the toilet tank, you noticed that the water level in the toilet tank is dropping slowly after it’s filled up.
You may wonder what’s causing this? And more importantly, how can you fix it?
In this article, we’re sharing with you the actionable steps to solve the issue on your own. Stay with us.
Reasons Behind Slow Water Level Drop in the Toilet Tank?
There are four main reasons why the water level in your toilet tank is dropping slowly. If your toilet tank is cracked, water will leak out slowly from the tank. As time progresses, the water level in the tank will begin to drop.
Another reason can be a faulty flush valve system. This system consists of the flush valve gasket, tank-to-bowl gasket, flush valve opening, discharge tube, and flush valve locknut.
All these components work together to create a strong seal that prevents water from leaking out of the toilet bowl.
However, if the flush valve system is faulty, water will slowly escape through the weak seal.
Another very similar reason is a faulty fill valve shank washer and/or locknut.
The shank washer and locknut also prevent water from escaping from the toilet bowl. If they are faulty, water will seep out through them.
The last reason for the slow water drop in the tank is a malfunctioning flapper valve. The flapper valve covers the flush valve system tightly and prevents water from going into the toilet bowl.
Only when the flapper valve is pulled, water is allowed to pass through the discharge tube into the bowl.
If the flapper is malfunctioning, water will pass continuously into the toilet bowl, leading to a running toilet.
How to Identify the Cause of the Dropping Water Level in your Toilet Tank?
We outlined above all the four major reasons why the water level in your toilet tank may drop slowly.
If you don’t identify the exact reason for the problem, you won’t know what exactly to fix. You may end up applying the wrong fix and the problem will persist.
The following steps will guide you on how to determine the cause of the dropping water level.
How to Know if You Have Leaks in the Tank?
As explained above, a cracked toilet will slowly leak out water. The crack may be very hard to see, but water will always seep around the cracked area.
Feel the body of the tank with your hand to find wet areas. If you also notice water seeping or dropping from the bottom of the tank other than the locknuts. It’s a sign of a cracked toilet tank.
The Solution to Toilet Tank Leak
If your toilet tank is leaking because it’s cracked, the only solution is to replace it with a new one.
Luckily, you don’t need a plumber to install a new toilet tank. The following steps will guide you:
- Stop the water supply to your toilet tank.
- Empty the toilet tank by pressing down the flush lever (or flush button) for a few seconds.
- Remove the tank lid and keep it somewhere safe.
- Remove the remaining water from the tank (if any) with a sponge.
- Disconnect the rubber hose from the inlet valve by turning the locknut anticlockwise.
- Look into the tank. There are two or three bolts around the flush valve. These tank bolts secure the tank tightly to the toilet bowl. Using a flathead screwdriver, loosen these bolts. You may use a wrench to loosen the complementing nuts under the toilet bowl.
- Remove the bolts and gently lift off the tank. You may need to loosen the bolts completely from the tank.
- Get a new tank of the same model. You can find the model number inner side of the toilet tank.
- Gently place the new toilet tank on the bowl, matching the holes.
- Replace the bolts and nuts. If they are rusted or you have cut them, get new ones. Connect the plumbing fixtures and fill the tank with water.
- Check if there is any leak.
In case these steps seem brief, read our guide on removing a toilet tank where we’ve covered this in detail.
How to Confirm if it’s Flush Issue?
If you notice water dripping around the flush valve locknut, a faulty flush valve system is the culprit.
Sometimes, you’ll only see a dirty buildup or rust ring around the flush valve locknut under the tank.
Sometimes, the dripping may be so much that it drops to the toilet floor. In either case, the flush valve gasket may be bad or the locknut is worn-out/damaged, creating a weak seal.
The Solution to the Flush Issue
The best solution is to change the entire faulty flush valve system. The system is entirely plastic and can deteriorate after long use.
Before that, you can try to tighten the flush valve locknut with a wrench if it’s loose. Turn the locknut gently clockwise to tighten it.
If tightening the locknut doesn’t work, try to replace the flush valve gasket with a new one. You would need to disconnect the toilet tank from the bowl to achieve this.
- Follow steps 1 to 7 from the last preceding section where we’ve described the tank removal process.
- Lay the tank safely on its back to access the flush valve system.
- Loosen the flush valve locknut by turning it anticlockwise.
- Pull the entire flush valve system off from the inside of the tank.
- Remove the faulty flush valve gasket and replace it with a new one.
- Clean the opening with vinegar or pumice stone and reconnect the fixed flush valve system.
- If the locknut is worn-out, install a new flush valve system.
- Insert the flush valve system off from the inside of the tank
- Set it properly in place and tighten the locknut.
- Gently place the toilet tank on the toilet bowl, matching the holes.
- Replace the tank bolts and nuts. Connect the plumbing fixtures and fill the tank with water.
- Check if there is any leak.
We have this covered in detail as well in the toilet leaking between tank and bowl article.
Is it Faulty Fill Valve Shank Washer and Locknut?
Check under your toilet tank. Do you notice water dripping around the fill valve locknut? A faulty fill valve shank washer and/or locknut is the cause if you notice water dripping.
Sometimes, the dripping may not be regular or obvious. But if you see a dirty buildup or rust ring around the fill valve locknut, you’ve got something to fix.
The Solution to the Faulty Fill Valve Issue
The best solution is to change the entire fill valve system. Before that as usual, you can try to tighten the fill valve locknut with a wrench if it’s slack.
- If tightening doesn’t work, the shank washer possibly needs a replacement. You don’t need to disconnect the toilet tank from the bowl to fix this.
- Stop the water supply to the toilet tank.
- Empty the tank, remove the lid, and remove any remaining water in the tank.
- Disconnect the rubber hose.
- Loosen the fill valve locknut by turning it in a counterclockwise direction.
- Pull the entire fill valve system off from the inside of the tank.
- Remove the faulty shank washer and replace it with a new one.
- Clean the threaded shank and opening with vinegar and reconnect the fill valve system. Set it properly in place and tighten the locknut.
- If the locknut is worn-out, get a new one.
- Connect the rubber hose and fill the tank with water.
Check if there is any leak.
How to Know if Flapper Valve Malfunction is the Cause?
If you notice that water is running into the toilet bowl without any human intervention, the flapper valve is malfunctioning.
This is obvious when the flapper is warped, hardened, or deformed. However, if the flapper is worn-out, water may drip slowly. You can still diagnose that using a colored toilet tablet.
Fill your toilet tank with water and drop a colored toilet tablet into the tank.
Allow the tank to rest for about 10-15 minutes. After that, check inside the toilet bowl.
Any sign of colored water in the bowl is also a confirmation that the flapper valve is malfunctioning.
The Solution to the Malfunction Flapper Valve
The best solution is to get a replacement flapper valve. But you can try the following sequentially to see if it gets fixed without spending money on a replacement valve-
- Stop the water supply to the tank, drain the tank, and remove the lid.
- Disconnect the flapper valve from the overflow tube and bring it out.
- Check the flapper valve carefully, feeling it with your hand.
- If the flapper lift chain is too loose or too tight, adjust it appropriately. Normally, it should be about a quarter-inch slack.
- Are there clogs and mineral buildup around the flapper and/or flush opening? If yes, clean that and the flush valve opening with borax or vinegar.
- If the flapper is warped, worn-out, hardened, rusted, or deformed, replace it with a new one of the same size and model.
- Connect the new flapper to the overflow tube. Make sure that it sits properly on the flush opening.
- Connect the lift chain to the toilet handle.
- Open the water supply to the tank.
- Conduct the “colored toilet tablet” test again to ascertain that the flapper is fixed.
For a detailed actionable step-by-step guide, read our take on fixing flapper valve issue.
Conclusion
There are several reasons why the water level in your toilet tank may drop slowly. But the good news is that most of those causes have easy and straightforward solutions that you can do by yourself.
While you do the troubleshooting, make sure to handle the tank and the internal components carefully.
All these components are brittle and can get damaged pretty quickly if not handled carefully.