Household Leak Detection

Customer with Inside Meters:

Some of our customers' water meters are located outside, under the ground. These customers cannot read their own meters to check for leaks.
However, if you have an inside meter (usually in the basement near the water heater or main turn-off valve) checking for leaks is easy.

  • Be sure no water is in use.
  • Look at the meter. If the red dial is moving at all, water is running in your home.
    • If that is the case, turn off your toilets one at a time and check the meter after each turn-off.
    • If a toilet is leaking, this process will allow you to pinpoint the source.
    • If the dial continues to move even after all the toilets are off, you should double check your faucets and hose bibbs.
  • Take a reading before retiring at night. Do not use any water during the night.
  • Read your meter again in the morning. If the readings match, there is no consistent leak at your property.

Toilet Leaks:

"Flapper Leaks"

Detecting Toilet Leaks Video

The flapper is a large rubber plug in the bottom of the toilet tank. The toilet tank is located in the back of the toilet where the unused water for the toilet bowl is stored. If you see or hear any water movement in the toilet bowl when it has NOT been used recently, you may have a flapper leak. To check for a leak:

  1. Carefully remove the lid from the tank and place it securely out of the way.
  2. Place a toilet dye pill (available from WSSC Water Communications Office at 301-206-8100) or a small amount of dark food coloring in the tank. Wait at least 20 - 30 minutes. If coloring comes through the tank into the bowl, WITHOUT FLUSHING, you have a leak. Repeat test every six months.
  3. Touch the flapper. If the coloring from your flapper gets on your fingertips, your flapper is deteriorating and needs to be replaced.

You Have A Leak Inside Your Toilet Tank If:

  • The lift wires and/or guide are corroded, bent, or hanging-up affecting proper flapper closing.
  • The valve seat (the receptacle for the flapper) is scaled or corroded

"Overflow" Leaks:

Examine the water level. If water is leaking into the top of the overflow pipe, the ballcock valve needs adjusting or replacing. If you are not sure if the water is spilling into the overflow pipe, place some finely ground pepper or baby powder along the walls of the toilet tank. If the powder moves toward the center, you have an overflow leak.

  • Adjust the float arm until the water level is 2" below the top of the overflow pipe.
  • Position the metal float arm slightly for desired water level.
  • On a plastic float arm, turn the adjusting screw located on the top of the arm.
  • If your toilet has a fluidmaster type ballcock valve, adjust the sliding clip.

"Siphon" Leaks:

Adjust the refill tube above the water line, 1/4" over the overflow pipe. Clip the tube to the overflow pipe to stabilize it so it does not insert deeply into the overflow pipe. The refill tube should never be "stuck down" into the overflow pipe.

Other Leaks

Outside Hose Bibbs and Faucets:

Hose bibbs and outside faucets are often left running -- particularly in the spring and summer when residents are away.  It is important to prevent someone from using your water without your permission. When leaving your home for an extended period, turn your outside faucet off from the inside valve to protect against water loss.  If you are unable to find this valve, please contact us. 

Hose bibbs and outside faucets are sometimes left on for protracted periods of time.  Common garden hoses can use up to 630 - 1,020 gallons per hour; larger hoses use more.  Since our water and sewer rates are based on an “average daily consumption” (ADC), the ADC and the amount of the bill may substantially increase due to extended outside water usage or water loss.

If you need help investigating your high bill concerns, please contact an agent weekdays between 7:30 a.m. and 7:00 p.m. at 301-206-4001, 1-800-828-6439, TTY 301-206-8345, or

Last Modified: