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What Happens When You Flush The Toilet While Showering?

Have you ever experienced a sudden change in the water’s temperature while you were enjoying a pleasant shower? Well, perhaps the issue here is a toilet flush from one of the other rooms.

So what happens when you flush the toilet while showering? Most homes have a trunk and branch plumbing system. The water in the showerhead shares water with the flush tank when someone flushes. Cold shower water is drawn into the toilet, giving out hot water. Also, a water pressure drop is seen.

However, there are easy solutions available to this problem. We will also cover the insights on it so you know why it’s happening in the first place. So without any further ado, let’s get started!

What Happens When You Flush The Toilet While Showering?

Your plumbing is most likely configured using a trunk and branch system. An easy method to test is flushing the toilet in your home. You will notice that it causes the water in the shower nozzle to become extremely hot.

Therefore, all water enters the trunk, narrows, and then is directed to specific branches in each room. Due to branch protocol, it redirects some of the water already being used in the bath area to secondary water use.

As a result, the shower must then share the cold water it was using with the toilet because it is asking for cold water. This causes your mixture to have insufficient cold water for the shower and to suddenly blast with hot water till the toilet tank is full.

Change In Pressure

On the other side, if your home has a weak water force, there will be less water for the other fixtures. Specifically, when one appliance uses a portion of the water from the branches. In certain homes, different appliances share the same bathroom’s single water supply line.

As a result, the same trunk line that supplies water to the bathing spot also supplies water to the toilet.

The showerhead receives reduced water flow when you flush the toilet. If your water flow system is not fast enough to refill the toilet tank, you will suffer. The shower’s rate of water flow is not fixed as long as the toilet tank is not getting filled.

Showering And Flushing: How To Maintain Them

Considering that everyone prefers their water at a comfortable temperature when showering, some issues can undoubtedly spoil the entire mood. Thankfully, there are multiple solutions available that you can apply to maintain hot showers.

1. Don’t Use The Flush When Someone’s In the Shower

Even though it’s common sense but certainly an efficient one. This is typically the simplest method. Moreover, depends on family members’ collaboration and is completely free.

Nevertheless, even the unforgettable family member might forget once in a while. So don’t be shocked if you still sometimes receive a burst of heated water when showering.

2. Reducing Water In The Tank

While it won’t entirely solve the issue, doing this will speed up tank filling and reduce the number of mishaps. Put a block or jug of water in the toilet tank to do this. The drawback is that your toilet won’t flush as smoothly and might have trouble draining waste down the drain.

3. The Shutoff Valve

The shutdown valve underneath the toilet can be turned to the midway position to accomplish a slowed-down refill rate. As a result, the toilet will fill more gradually and have less impact on the shower’s temperature.

4. Thermostatic Mixing Valve

For assistance in balancing your hot and cold water, you may install a thermostatic mixing valve monitor. Keep the water temperature for the shower at a level that is both secure and cozy by using thermostatic mixing valves. It automatically regulates the amount of hot and cold water.

5. Increasing Water Availability

This issue can potentially be resolved by increasing the amount of water that is accessible in your plumbing system. However, it will necessitate a substantial plumbing system change.

Nevertheless, you can increase the diameter of the trunk pipe and the branch pipe if you have a trunk and branch system. All plumbing fittings will have more water accessible to them as a result.


You’re now close to becoming a plumbing engineer. So to ease it, let’s look into some frequently asked questions.

How long does the shower water remain hot after a toilet flushes?

As soon as the toilet tank is refilled, your shower’s water pressure returns to normal. It now relies on the flow rate of the branches. Shower water begins to recover and return to normal as soon as the toilet tank is filled.

How are showers and toilets connected?

The water supply is the same for both if your home has a trunk and branch plumbing system. As a consequence, sharing the water that has been stored. So when one requests water, the other receives less.

Is increasing the diameter of the branches effective?

Increasing the diameter of the branches is one of the solutions that are available in your hands. This will allow more water to pass through the branches and provide enough water for all.

Can any other thing affect showers except toilet flushes?

Anything that requires water to function can affect the water received in the shower. For example, a washing machine. Your water heater may not be able to handle the demand created by putting a load of laundry in the washer.


Let’s give you guys a recap of what happens when you flush the toilet while showering. First, the temperature of the water in the shower is changed. So, you won’t be getting warm water in the shower like before. Similarly, the water pressure is also decreased as a result of excess demand compared to supply.

Nevertheless, installing a thermostatic mixing valve and upgrading the plumbing are the two most effective ways to address this issue. At the same time, the simplistic solution is to ask family members to hold off on flushing while you are in the shower.