What Happens When You Flush the Toilet While Showering?

When someone flushes the toilet as you enjoy a soothing shower, you will notice a cold or hot water blast. This can be a painful experience, especially if you never expected it. Dealing with the issue can be complicated, mainly when living in a household of many.

When you flush the toilet while showering, the toilet will pull cold water to refill the tank. This increases the amount of hot water in the shower leading to a hotter shower for a while. The water pressure in the shower also reduces. The normal shower resumes when the toilet tank fills.

Fortunately, this post will explain exactly how it happens and how it can prevent this problem.

Does Flushing the Toilet Affect the Shower?

Yes, a drop of water pressure in the shower makes the shower heat. This occurs because the plumbing system comprises a trunk and branching system. Water runs from one building sector through a large pipe connected to other plumbing fixtures such as your sink, shower, faucet, and toilet. 

If your plumbing has low water pressure, one fixture acquires much water from the main pipe, making other fixtures get less water. In most cases, many homes have a major water supply line that connects to the tub, shower, and toilet within the same bathroom.

Therefore, the toilet tank needs water to fill it after flushing. Since the toilet uses the same water as the tub or shower, flushing the toilet will lower the water pressure, making less water flow into your shower or bathtub.

How to Prevent Flushing the Toilet from Affecting the Shower

Even though flushing the toilet often affects the shower, you can easily maneuver this problem. Here are top fixes for preventing a toilet flush from affecting your shower:

1. Regulate the Toilet Supply Valve

If your toilet has an old-design ballcock valve, you can regulate the water level in the tank to prevent a flush from affecting the shower. The ballcock valve is a float-controlled device that determines the amount of water flowing into the tank. However, you can replace the toilet valve if it is unadjustable.

To increase the water level, turn the adjusting screw clockwise. Also, turn it counterclockwise to lower it. Finally, test your adjustments by flushing the toilet as the shower runs and checking for water flow changes or temperature changes.

2. Install Thermostatic Mixing Valve Monitors

You can also install thermostatic mixing valve monitors that help balance cold and hot water. These valves automatically regulate the amount of cold and hot water, maintaining a comfortable and safe water temperature for the shower. 

They maintain a consistent shower temperature even when water runs through other plumbing fixtures including your toilet.

3. Avoid Flushing the Toilet When the Shower is in Use

This is an obvious solution, and there is no need to flush the toilet when the shower is in use as it can alter the water temperature in the shower. You can easily control this habit depending on the cooperation of your family members. 

If your house has separate bathrooms, try encouraging other family members to avoid flushing the toilet when the shower is in use.

Also, you can design and place a sign at the bathroom door to act as a reminder. If you have one bathroom, you can consider investing in a dual flush toilet with a low-flush option for non-solid wastes or a low-flush toilet with minimum water for each flush. 

However, when using this solution, remember that courteous family members can occasionally forget and flush the toilet when the shower is in use, making the user suffer from temperature changes.

4. Invest in a Load Balancing Manifold

You can consider installing a load balancing manifold if you have a multi-head shower. This will ensure that each head acquires constant water pressure, helping to prevent scalding. 

The manifold eliminates the branch and trunk system with a line for each shower, toilet, and other plumbing fixture. The manifold is connected directly to your water heater and distributes hot water to each dedicated fixture. It is also connected to the main cold water supply line. 

This appliance ensures a constant water temperature in your shower even when someone flushes the toilet since each fixture has its supply. It would be best if you called a professional plumber to install the manifold system.

5. Lower the Quantity of Water in the Toilet Tank

If you have an old toilet, you use lots of water for every flush. You can lower the amount of water used for every flush by investing in a low-flow toilet or regulating the fill valve to reduce the water in the tank. You can also preserve water by ensuring you only run the shower when it’s in use.

In addition, you can  consider placing a jug or brick of water in the toilet. The brick will occupy space in the toilet water tank, leaving little room for water. However, you may also experience changes in water temperature that will last for a short time. In addition, your toilet may face a weak flush and eventually overflow.

6. Increasing the Water Available

Increasing the amount of water available in your plumbing system can also alleviate this problem. However, it will require a significant alteration of your plumbing system. 

If you have a trunk and branch system, you can increase the diameter of the trunk pipe and/or the diameter of the branch pipe (if the branch supplies the whole room). This will increase the amount of water available to all plumbing fixtures.

7. Modify the Plumbing

If some water remains in your toilet tank after you flush, it could be because the fill valve cannot maintain the amount of water required for a full flush. You can consider repairing or replacing the valve or the whole toilet for this problem. 

For best results , you can research the best flushing toilets available in the market to find the perfect toilet for your needs.


Why Does a Toilet Flush Heat the Shower?

When a toilet is flushed when the shower is in use, the toilet tank requires water to refill. At this time, the branch supplying water to the toilet will not have enough water as you shower. Therefore, your toilet will pull water from the shower. 

The toilet tank fills with cold water from the supply line and leaves you with hot water in the shower. This can be very uncomfortable, especially when trying to unwind and relax in a shower or hot bath.

What Makes Flushing the Toilet Affect the Shower?

There are many reasons why flushing the toilet affects the hot shower. The main reason is that a toilet flush leaves the shower with less water accessible since the toilet is pulling water available for the shower.

What Happens When You Flush the Toilet When the Shower is Running?

Various things might happen when you flush the toilet when someone is using the shower. Some possible outcomes include reducing the water temperature in your shower by pulling water from the shower to fill the tank or causing pressure differences that lead to colder water passing through the tap.


It can be quite frustrating to experience temperature changes in your shower due to a toilet flush. Thus, you should know the outcomes of flushing the toilet while using the shower to curb this problem. 

There are many ways to prevent this, including changing your plumbing system, increasing the amount of water available, and installing a thermostatic mixing valve. Thankfully, all these fixes will ensure you enjoy a calm shower even when someone flushes the toilet.

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