Why Does My Toilet Water Backup Into My Shower?

Plumbing problems in your home can be a major point of frustration, especially when it comes to something like toilet water backing up into your shower. This is unpleasant, odorous, and highly inconvenient. This wastewater is also potentially harmful to your health.

If toilet water is backing up into your shower, this is most likely due to a clogged sewer line. If something is blocking wastewater’s path, preventing it from reaching the sewage lines, it has no choice but to start backing up through your shower drain.

While this occurrence can be highly unpleasant and cause a certain degree of distress, there are several ways to address the problem and prevent it from occurring again. You will need to start by finding the source of the clog and removing it. You will need to take precautionary measures to ensure the issue does not re-occur.

Why Does My Toilet Water Backup Into My Shower?

When the sewage system is working properly, the toilet will direct its wastewater into the sewer line. Your home’s sewer line will then transport the wastewater to the main sewer line. If something is blocking the wastewater outlet, the waste cannot move through the system towards the main sewer line.

As a result, the wastewater will have no choice but to start backing up the pipe, ultimately coming back up through the path of least resistance – the shower drain. The shower drain inherently offers less resistance than the toilet drain. This is due to the water at the bottom of the toilet and the overall design of the toilet trap.

The toilet is generally set higher up than the shower, so the water will be far more likely to move up through the shower drain than come up through the toilet again.

It’s important to differentiate between the main sewer and the secondary lines. Remember that your plumbing system functions almost like the branches of a tree. If the cause of the blockage is in the main line, you will most likely have water coming up through all the drains in the home instead of just the shower.

If water is only coming up through the shower, the problem is most likely in your secondary piping. Thankfully this will make it easier to address the problem, as the clog is most likely situated within easy reaching distance of the house.

Several causes of blockages and several methods to address these will be discussed in detail under the headings to follow.

Causes Of Clogged Pipes

There are several reasons your pipes could be blocked, thus causing the toilet water to back up into your shower. If you can successfully identify the issue, you can ensure that it will not re-occur. However, it may sometimes be difficult to find the root cause of the problem without professional help.

clogged drain pipe
Image from Nathan Gebben

Sometimes the material from which your piping is made can cause major issues. For example, old cast iron piping can rust and break down. Terracotta piping is also prone to failure with time, as it can crack and cause other problems.

Soil failure is another possible cause of clogged pipes. This will also effectively prevent the wastewater from flowing as it should through your sewage lines.

Tree roots are another source of sewage line blockages. As tree roots always gravitate towards a water source, they may slowly find their way into your underground piping through small cracks. Once they grow and establish themselves inside the pipes, they will cause a major blockage.

Fat, oil, and grease are other culprits that frequently cause blockages in sewage pipes. While these substances generally begin as liquids when poured down the drains, they will quickly coagulate and form a solid substance. This is especially prevalent in colder climates where fat, oil, and grease will freeze solid inside the piping, blocking water movement altogether.

Many people underestimate how our hair can cause major blockages of sewage pipes. Humans generally lose between fifty and one hundred hairs per day. This hair can quickly get sucked down into the drains, eventually forming clumps that cause complete blockages of the pipes.

Hard water can potentially cause blocked pipes. Because hard water has high levels of dissolved minerals such as calcium, this can eventually cause a major limescale build-up on the inside of the pipes, ultimately blocking them. Suppose you find that limescale is the cause. In that case, you will benefit from installing a water softener to prevent a re-occurrence.

Generally speaking, flushing anything down the toilet that shouldn’t be flushed will cause the sewer pipes to become blocked. This includes sanitary pads, diapers, and even flushable wipes.

person using toilet plunger to remove an object from the toilet trap

How To Prevent Toilet Water Backing Up Into Shower

To prevent the toilet water from continuing to back up into your shower, you will need to remove whatever is clogging the pipe. Before attempting any fix, turn off the water mains.

Your first option to fix the problem is to use a plunger. This simple solution will help unblock the pipes if the blockage is relatively small and not completely stuck in place. Alternatively, you could use a plumbing snake to locate and dislodge any blockage that does not respond to your plunger use.

It’s always good to check the vent pipe in these cases, as the vent pipe can potentially have a build-up of leaves and twigs that will also hinder the effective movement of water thanks to a pressure build-up.

There are several home plumbing remedies you can try to unblock your pipes. Some of these include a simple solution of dish soap and hot water. Alternatively, you can use a combination of salt, Borax, and vinegar to break down the blockages.

vinegar and baking soda in two bottles

Baking soda combined with vinegar, salt, cream of tartare, or lemon juice can also be a highly effective remedy.

If none of the above fixes are effective and your toilet water is still backing up into your shower, you should consult a professional. They may resort to hydro-jetting or another similar professional method of de-clogging your pipes.


If your toilet water is backing up into your shower, it is most likely a result of a blocked sewage pipe. To fix the problem, you will need to attempt to de-clog the pipe using one of the methods outlined above. Once you have identified and fixed the problem, you will need to put measures in place to ensure the issue does not re-occur. If you find you cannot fix the issue yourself, call in the professionals to assist you.

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