Toilet Bowl Water Level Drops Overnight: 6 Easy Fixies

It’s not an uncommon situation when you go to sleep one night, only to wake up the next day and find that your toilet’s water level has dropped. But what does it mean? Is it something I should be concerned about?

When the water level drops in a toilet, it may indicate several potential issues with the toilet bowl or attached drain pipes that may need addressing before they become serious, resulting in leaking and more expensive repairs.

So in this article, we’re going to cover all the main things that might cause a toilet bowl’s water level to drop, as well as how to fix it.

Why is your toilet bowl water level dropping?

One of the challenges when fixing a dropped water level in a toilet bowl is that quite a few potential problems can cause this, which range from a simple and easily fixable problem such as an incorrectly set fill valve which can easily be adjusted in a few seconds with a screwdriver.

But it may also indicate more serious damage that needs more comprehensive component repairs or replacements.

The ideal water level should be one to two inches in depth. If you’re dropping below that (even just temporarily after flushing) and experiencing a loud gurgling sound when you flush, you may have a problem and should keep reading to find out what that is.

Flapper/flush valve problems

The flush valve is the most common point of failure on a toilet. Fortunately, it’s relatively easy to self-diagnose and fix on the cheap if you follow our instructions. So hold fire on calling the plumber just now, as you may find that your flapper’s at fault here.

What is a flapper?

The flapper or flush valve essentially acts as a rubber valve that sits in between your toilet’s tank and the bowl. Pulling down on the handle lifts a chain connected to the flapper, allowing water to flow down from the toilet tank and into the bowl.

It’s a simple process and, as such, is not too difficult to diagnose and fix by yourself.

There are two main methods to diagnose a flapper problem. The first is if the toilet doesn’t seem to flush completely unless you hold the handle down for an extended period, it’s usually because it’s not being appropriately lifted from the toilet tank base. This is caused by the connecting chain being too long.

Also, if you find that it seems to flush just fine but continues running, it may indicate that the valve is not creating a good enough seal. This could be due to damage or wear and will usually require replacing the flap (don’t worry, they’re cheap).

Once you’ve fixed your flapper, you should find that the water level in the toilet becomes more stable.

A clogged drain vent

Your toilet does not just have a single path that drains water directly to the sewer. They also link to a vent that leads to the roof of your house. This is a vital part of maintaining the water level because the negative pressure caused by the vent is what allows the toilet to flush.

So when this gets blocked, it can prevent the draining system from working correctly and may need to be cleaned out to restore functionality to the flushing system and water level.

Incorrectly set water level

Another easily fixable yet often overlooked problem people run into. Within your toilet’s tank is a ‘fill valve’ that determines the toilet’s water level. A screwdriver can easily adjust this to set your desired water level.

In some cases, this fill valve may have become faulty, which is why your water level is dropping. So, in this case, it will need replacing.

Damaged seals

The toilet seal, or ‘wax ring,’ is designed to create an airtight seal between where the toilet meets the floor. This seal needs to remain in good condition for all the water to be drained into the sewer.

So when this seal goes bad, you may find it starts to leak bad-smelling water over the floor. Or if your plumber has caulked the base of the toilet, you will find that the water collects inside the toilet and cannot escape.

It will require the toilet to be lifted, everything cleaned, and a new wax ring should be installed to ensure all the water can correctly escape.

Damaged/cracked bowl

Toilet bowls are generally pretty tough, and it’s usual to see them crack without a significant impact. Nevertheless, it can happen and often result in water escaping from the bowl, thus lowering the water level.

Inspect the entirety of the bowl for any cracks or signs of a toilet leak. If found, the easy solution is to replace the whole thing.

Non-flushable object problems

Certain products should not be flushed down the toilet. For example, not every kind of tissue type should be flushed, as well as things like tampons.

If these items are discarded into the toilet but cannot flush away correctly, they can become lodged in the drain pipe. They will start to siphon water from the bowl level overnight without you realizing it.

The drain pipes will need to be unblocked and these products removed. 

Then, it requires some user care to only ever flush products intended to be flushable.

How to stop toilet bowl water level from dropping overnight.

Now that you’ve been able to diagnose the root cause of the problem, it’s time to get it fixed.

Fortunately, in almost all of the most common cases, this is something you can solve yourself at minimal expense. Here’s a rundown of how to go about fixing these problems.

1. Fix or replace the flapper valve

Two primary issues occur with the toilet flapper valve. The first is that the chain is too tight, meaning it doesn’t close properly and allows water to leak out slowly. Or, it may be too loose, meaning it doesn’t lift enough to let the water bowl refill after flushing.

Either way, you can remove the toilet tank cover and check the chain length. These chains are exceptionally cheap and can easily add or remove a few links with some pliers.

If the toilet flapper is leaking, worn, or damaged for some reason, replace it with a new one. They are also very cheap and easy to install yourself.

2. Cleaning the air drain vent

This one’s a bit more challenging and requires a trip up to your roof to clean it. If you don’t feel confident doing this, we recommend getting a professional out.

The process itself is relatively simple. You clean out the vent entrance of debris, such as leaves/twigs, that can often get blown into it. Then, pouring cold water down to flush everything is a good idea.

If there are more severe blockages further down the air vent, you may need a cleaning pipe that can reach far enough down and extend around the sharp corners in the vent path.

3. Adjust the toilet level

Take a screwdriver and adjust the fill valve. You can turn it clockwise to raise the level and counterclockwise to lower it.

Try only to do a half-turn each time and inspect where the new level sits before adjusting it again.

4. Replace the wax ring seal

This is a bit more involved and will require a professional. But if the wax ring has gone bad and is leaking water, the toilet will need to be lifted, and any caulking seals around the base will break.

Then the old wax ring gets removed and replaced with a new one. Then the toilet itself can be reinstalled.

5. Replace a damaged or cracked bowl

If replacing the wax ring did not solve the toilet leak causing the water level to drop, the issue is most likely with the bowl itself.

If the crack is clearly visible, it can be repaired in certain situations. But this presents a weak spot in the toilet, so we recommend replacing the entire bowl.

6. Removal of non-flushable objects

When non-flushable items have become lodged in the toilet and are siphoning water off and lowering the level, you will need to use specialized equipment to remove them.

This device is called a plumbers snake and can feed around the tight water pipe bends to remove objects.

This is not worth investing in for this minor issue; you should have a plumber come and remove them.

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