Nothing disrupts a nice warm shower like an unexpected temperature shift when someone flushes the toilet. If your shower gets hot after a toilet is flushed, it can be more than annoying; it may actually hurt you if the temperature fluctuation results in scalding hot water coming out of your showerhead. And it’s not just hot water you could get hit with in the shower. Cold water can sometimes surprise you, too, when a toilet flushes or if certain appliances are running.

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But how does flushing the toilet affect the shower? If this issue is occurring in your home, it probably involves your water pressure and the configuration of your pipes. Luckily, this annoyance is something that can be remedied without spending too much time or money.

Someone Flushed the Toilet — Why Does the Shower Get Hot?

So, why does flushing the toilet affect the shower? Without getting super technical, most homes use a plumbing system with pipes arranged in what’s called a trunk and branch system, which is just like it sounds: Bigger, main pipes are the “trunk” that then send water out to the smaller branches. The branches are what connect to the sinks, toilets, showers, dishwashers and other fixtures in your home. Temperature fluctuations like hot water in the shower when the toilet flushes occur when the water pressure is unstable and pulls water from one branch or appliance that’s being used to another.

While there are bigger plumbing projects you can tackle to address this issue, like widening the trunk or installing a more complex, well-balanced system, there are simpler ways to fix the problem. If you’re in the market for an easy and affordable fix, you can either install a thermostatic mixing valve to your shower or adjust the supply valve on your toilet.

A thermostatic mixing valve will keep a check on the water pressure of both the hot and cold water supply lines entering the shower before the cold water mixes with the hot. If the pressure of one drops, it will adjust the other accordingly to help keep the shower temperature consistent, in spite of any toilet flushing action occurring elsewhere in the house.

Another way to tackle this issue is to limit the water flow to your toilets. You can do this by closing the toilet supply valve a bit. Doing so will cause your toilet to fill more slowly, but it will help minimize the temperature fluctuations in other plumbing branches, like your shower.

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Why Might the Shower Get Cold When Someone Flushes the Toilet?

A blast of hot water is not the only sudden temperature shift you may experience in the shower. Flushing the toilet can make the shower cold too. This can also happen when you start running another tap or appliance, like a washing machine or dishwasher, that requires water and thus disrupts the water distribution and pressure of your shower. Luckily, you can deal with the issue in the same way that you’d address the hot water problem, so that your water temperature woes can be solved in one fell swoop.

Flush Freely

Water in the shower is meant to stay at a comfortable temperature of your choosing. Sure, cold showers are trending, but any cold or hot blasts to shock the system should be up to you, and not an unfortunate side effect of your home’s imbalanced plumbing. If you feel like updating your plumbing to a more sophisticated system that solves the problem, by all means, do so. But you can also try fixing the issue with much simpler, more affordable strategies that will help keep your water pressure balanced. By installing a thermostatic mixing valve to your shower and/or adjusting your toilet supply valve, you can easily take control of your shower temperature and steer clear of both hot and cold surprises while you bathe.

Hard water is water that’s high in dissolved minerals like calcium and magnesium. It can cause a wide range of problems in your home, like affecting the taste of drinking and cooking water, staining toilet bowls and sinks and damaging appliances like washing machines and hot water tanks.

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If your home has excessively hard water, the best solution is to install a whole-home water softener. The most common type of residential water softener is an ion-exchange system, which uses negatively charged resin beads to attract the positively charged minerals before exchanging them with “softer,” positively charged sodium or potassium chloride. Then, the softer water is dispensed into your home’s water supply.

Installing a water softener requires considerable comfort with DIY projects and some plumbing knowledge that goes beyond the basics, so it’s not a suitable project for every homeowner. That said, installing a water softener yourself can lead to substantial savings over having it professionally installed.

If you feel up to the task, follow this basic installation guide.

Before You Begin

Before you commit to installing a water softener, verify that your water actually needs to be softened. While hard water has many deleterious consequences, soft water can prematurely corrode pipes and elevate the sodium levels of your home’s drinking water. Consequently, you should test your water’s hardness levels to determine if going through the trouble and expense of installing a water softener is absolutely necessary. You can contact your local water company to see if they have your water supply’s hardness level on file, or you can purchase an at-home hard water test kit. In either case, softening your water should only be necessary if your water hardness exceeds 7 grams per gallon.

Once you’ve determined that you actually need a water softener, figure out where you’re going to install the unit. It should be installed as close to where the main water supply enters your home as possible, which is often in a garage or basement. Additionally, it should be installed before the water line reaches your home’s hot water heater so that the tank and hot water lines don’t become contaminated with hard water.

Next, ensure that the area you’ll be installing the unit is large enough to accommodate both of the softener’s tanks. Most water softeners have a “mineral tank” that houses the resin beads and a “brine tank” that contains the salt or potassium chloride. These tanks need to be installed side-by-side. The installation location also needs to be near an electrical outlet to provide power to the unit and within reach of a drain such as a utility sink or floor drain.

Finally, if anyone in your household is on a low-sodium diet, use potassium chloride salt in the brine tank instead of sodium chloride, which is common table salt.

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How to Install a Water Softener

What You’ll Need

• Screwdriver
• Tape measure
• Flexible water supply line
• Adapter for flexible supply line
• Copper pipe and fittings
• PVC pipe and fittings
• Hacksaw, copper pipe cutter, or PVC cutter)
• Solder flux and blow torch

Step 1: Install a Bypass Valve

Most water softeners come with a bypass valve that lets you shut off the water supply to the unit when it needs to be serviced while still allowing water into your home. It consists of two valves: one where the main water supply line enters the unit, and the other where the softened water exits to be transported into your home. Press the valve into the corresponding port on the back of the control module (the box that houses the LCD display screen) and secure it in place with the provided clamps.

Step 2: Shut off the Water

Locate and close the shut-off valve to your home’s main water supply. Drain the water out of your home’s water lines by opening a sink faucet until water stops flowing.

Step 3: Tie Into the Water Supply Line

The two most common ways to connect a water softener to your home’s main water supply are by hard-piping it with rigid copper or PVC pipe, or by using flexible supply lines similar to those used on washing machines and hot water heaters. The type you use may depend on your local building codes, the type of pipe your home’s main water line uses or personal preference.

Sections of copper plumbing pipe and fittings can either be soldered together with solder flux and a blow torch, or connected with push-fit fittings like SharkBite connectors. When soldering copper, you should cut and preassemble the pipes and fittings before installing them onto the water softener, because the heat from the blow torch can damage the softener’s plastic components. Flexible supply lines are often the easiest to use since they don’t require any cutting or pre-assembly, but you may need to use a special adapter to connect the flexible line to your water supply line and/or the water softener’s bypass valve.

Use a copper pipe cutter (for copper pipe), PVC cutter (for PVC pipe) or hacksaw (for either) to make two cuts into the main water supply line. One cut should be to one side of the softener where the water line first enters your home, and the other cut should be to the other side of the softener where the line continues into your home.

Install the water softener’s water supply lines onto both sides of your home’s main water supply line using the appropriate fittings and adapter. The type of fittings and adapters you’ll need will depend on the type of pipe used for the main water and water softener lines. The pipe connected to the main water supply where it first enters your home should be installed on the inlet side of the water softener’s bypass valve. The pipe connected to where the main line continues into your home should be installed onto the outlet side of the softener.

Step 4: Fill and Connect the Tanks

Connect the mineral tank to the brine tank with the provided tubing and clamps. Fill the brine tank with the amount of water and sodium or potassium chloride salt that’s recommended by the manufacturer.

Step 5: Connect Drain Tubes

Most water softeners require a drain hose that transports the discharge water from the mineral tank during its backwash cycle, and an overflow drain connected to the brine tank to prevent the tank from overflowing onto the floor. Both drain tubes can go to the same drain, but they can’t be connected together. Connect the drain tubes to each tank and run them to the closest drain.

Step 6: Turn the Water and Start the Unit

Partially open the main water supply valve to your home until it’s in the 1/4 position, and allow trapped air in the line to escape. Once you can hear a steady stream of water running into the tank — without any hissing sounds that indicate air is still escaping — you can fully open the main water valve to begin filling the mineral tank.

Plug the unit into the nearest electrical outlet and turn on the control module. Follow the startup procedure on the screen, which will often involve setting the time and desired water hardness level.

Step 7: Run the Backwash Cycle

Run a backwash cycle to purge the remaining air from the system and loosen the resin beads in the mineral tank. While the backwash cycle is running, inspect all the plumbing lines and connections for leaks. Once the cycle is complete, check the brine tank and adjust the brine solution as necessary.