I Lose Water Pressure When I Flush My Toilet: What Is Wrong?

Toilets inside the home are connected to the main water line. This makes them susceptible to drops in water pressure; it may also be the case that the toilet causes drops in water pressure when it is flushed. Understanding more about the causes and fixes for these problems will help you find a solution that keeps your toilet running.

Toilets use water pressure to refill the tank.

The Problem

Toilets are connected to a supply line that taps into the main plumbing system. These lines are usually 3/4 inches in diameter, which means they are the same size as most of the largest pipes in your home's water pipes. When the toilet flushes, they draw from the main water supply. This will decrease the amount of pressure that's available to the rest of the pipes in the house. The effect will only last as long as it takes for the tank to refill, however.

Diagnosing Low Pressure

Water pressure can drop for a number of reasons, including new construction nearby, sprinklers turning on or problems with the water utility's delivery system. It's important to test the toilet to see whether the flushing action really is causing the low water pressure. Turn on the cold water as high as it will go in the bathroom sink. While the water is running, flush the toilet. If the water pressure has a noticeable drop in pressure as soon as you flush, the toilet is the cause of the low water pressure. If the water pressure remains steady, the problem is elsewhere.

Tips for Dealing with Low Pressure

Because the toilet tank fills over a period of about 30 seconds, that's about as long as the pressure drop will last. The simplest way of dealing with this problem is to not use other devices that require water while your are using the toilet. For example, wait to run the dishwasher, or pause the dishwasher while you are using the bathroom. Setting the sprinklers to turn on during a time when people typically are not using the bathroom will also increase the overall amount of water pressure in the home during peak usage times.

Increasing Overall Water Pressure

If you want to increase the overall amount of water pressure that's always available to the home's plumbing system, it's possible to adjust the water pressure regulator valve. This device is located along the main water line in the house and controls the pressure that's released to the entire system. Loosen the nut at the base of the adjustment valve and turn the nipple on top with a screwdriver to change the pressure settings. Most homes are set at about 60 psi, but you can safely increase the pressure to about 80 psi. This will provide more steady pressure when the toilet flushes.