Taste and odor in drinking water

Links to items below: HighlightsWhat can cause an earthy or musty taste and odor?How does OWASA remove earthy/musty taste and odor? How long will earthy/musty taste and odor last? What can customers do about earthy/musty taste and odor?What causes chlorine taste and odor in March and early April?What can customers do about chlorine taste and odor?Odor from pipes under sinks, etc.Phosphorus and nitrogen in lake water

Highlights

  • Odor and taste may be present in our water due to factors discussed below. Odor and taste do not make water unsafe, and we use several methods to resolve taste and odor.
  • We are committed to providing water which is healthy, safe, and aesthetically pleasing.
  • If you are concerned about our water quality or wish to report taste or odor, please contact our Jones Ferry Road Water Treatment Plant Laboratory staff at (919) 537-4228 or wtplaboratory@owasa.org. We will be glad to test our water at your home or business at no charge.
  • Our water may have an earthy or musty taste and odor because of compounds produced by algae and compounds stirred up by mixing of water layers in our lakes in the autumn.
  • We monitor the levels and types of algae in our lakes and change our water treatment processes when needed to resolve taste and odor. We also test our drinking water thousands of times each year to check that it is safe.
  • In March and early April, our water may have chlorine taste and odor because of our annual change in chlorine disinfection in March. Chlorine taste and odor can be neutralized with lemon juice and by other means discussed below. (In months other than March, we disinfect with a compound of chlorine and ammonia which has minimal or no chlorine taste or odor.)

What can cause an earthy/musty taste or odor in drinking water?

From spring through fall, an earthy or musty taste or smell may result from compounds produced by algae growing in our Cane Creek Reservoir or University Lake. Algae and other aquatic plants are common in lakes.

These plants normally grow most in the warm to hot months of the year. Growth of algae is related to factors such as a warmer than normal winter, rainfall, sunlight, and levels of phosphorus and nitrogen compounds in lake water.

Some people can notice odorous compounds from algae at levels as low as 5 parts per trillion; one part per trillion is like one drop of water diluted into 20 Olympic-size swimming pools.

Although our drinking water treatment process removes algae, some taste and odor-causing compounds may remain. The compounds are harmless, but are noticeable to some people at very small levels as noted above.

During the fall, as the surface of the lakes cools to the same temperature as the bottom waters, mixing of the water layers occurs. This stirs up sediment that can contain compounds with taste and odor.

How does OWASA remove musty/earthy taste and odor from water?

We add a chemical (called permanganate) to water as it is pumped from our lakes. This substance neutralizes taste and odor causing compounds.

As the lake water enters our Jones Ferry Road Water Treatment Plant, we add powdered activated carbon for additional removal of taste- and odor-causing compounds. “Activated” means the carbon has been treated to increase the surface area and thus the ability for taste and odor compounds to adsorb (or stick) to the powder activated carbon.

OWASA and other utilities routinely use powdered activated carbon and permanganate in water treatment.

We test our water when needed to identify the compounds which cause taste and odor.  We use the test results and other data in making water treatment decisions.

When water with significant taste and odor is in our 390 miles of water pipes, we release water from fire hydrants to remove water with taste and odor and replace it with fresher, better tasting water. This “flushing” is done when water leaving our treatment plant has normal or close to normal taste and odor.

How long does earthy/musty taste and odor last?

The answer depends on conditions including the level of algae and odorous compounds in our lake water.

The transition will be gradual and customers may continue to experience taste and odor for several weeks.  The taste and odor can remain noticeable in our water throughout our service area even after the water leaving the Jones Ferry Water Treatment Plant has little to no taste and odor.

The length of time it takes for the taste and odor to improve can vary throughout our service area.  This is due to mixing of the fresher, better tasting water with water that has a noticeable taste and odor within our 390 miles of drinking water pipes and our water tanks, which hold 6.5 million gallons of water. Some people can notice odorous compounds at levels as low as 5 parts per trillion; one part per trillion is like one drop of water diluted into 20 Olympic-size swimming pools.

Once the water leaving our water treatment plant has less noticeable taste and odor, we release water from fire hydrants to accelerate the replacement of water that has a noticeable taste and odor with water that has a better, less noticeable taste and odor.

Customers may need to flush their internal plumbing once the water in the OWASA pipe serving the area has less noticeable taste and odor.  Some customers minimize hot water use during taste and odor events.  If this is the case, noticeable odor may linger in hot water due to continued, slow mixing of water with noticeable odor in the hot water tank with fresher, better smelling water. Flushing the water heater according to the manufacturer’s instructions once fresher water with less noticeable taste and odor is available will help resolve this issue.

What can customers do about earthy/musty taste and odor?

  • Add a slice of lemon to water in a pitcher or other container.
  • Let a container of water sit in a refrigerator until the water is chilled.
  • Filter water with an activated carbon filter.

What causes chlorine taste and odor in March and early April?

We normally disinfect our drinking water with a compound of chlorine and ammonia (“chloramines”) to kill bacteria during our treatment process and minimize the potential for bacterial growth in our 390-mile water pipe system and in our customers’ homes and businesses. Chloramines have minimal taste and odor.

Chlorine taste and odor is noticeable in March and early April because we disinfect in March with chlorine in the form of liquid bleach, which has more odor than chloramines. We make this disinfection change one month per year to provide a more intense level of disinfection as recommended by the US Environmental Protection Agency and NC Department of Environmental Quality. 

We regularly test the levels of chlorine and chloramines in our water and we follow Federal and State standards for the minimum and maximum levels of these disinfectants in the water system.

Link to a notice of chlorine disinfection in March

What can you do to remove chlorine taste and odor?

  • Filter water with an activated carbon filter.
  • Let water sit in a refrigerator for about a day so chlorine will have time to dissipate from the water.
  • Boil water for one minute to evaporate the chlorine.
  • Add a few lemon slices to a pitcher of water. The lemon has ascorbic acid, which neutralizes chlorine. 

Odor from pipes under sinks, etc.

Odor may rise up from a sink drain. The pipe under a sink can collect debris which creates odor. If you smell an odor at a sink or other drain, fill a clean glass halfway with tap water and smell the water in a separate room or outdoors. If the odor is no longer present, the odor source is likely the drain beneath the sink. We recommend pouring bleach down the drain and cleaning the drain to remove debris and odor. If the odor is not from the sink or the problem persists, please contact our Water Treatment Plant Laboratory staff at (919) 537-4228 or wtplaboratory@owasa.org

Toilets, floor drains, and sinks have a p-trap (a u-shaped pipe which holds water) to prevent odorous air in drains and sewers from rising up through the drain into a home or business.  If a toilet, sink, or drain is not used for a long time, the p-trap may go dry from water evaporation and allow odor to enter a building.  To refill a p-trap, pour water down a floor drain or run water in a sink. Please click here for more information about p-traps. A p-trap may also go dry if it has a leak. Leaks should be fixed so that odorous air will not rise up through the drain.

More about phosphorus and nitrogen compounds in lake water

Phosphorus and nitrogen compounds may be present in a watershed due to agricultural, business, and residential use of fertilizer, due to animal waste stored in lagoons, and other factors.

Phosphorus and nitrogen are key components of fertilizer because they are nutrients which encourage plants to grow.

If too much fertilizer is used or improperly applied, stormwater can wash nutrients into nearby streams, rivers, ponds, or lakes where the nutrients cause algae to grow.

Excessive algae in a lake may make water treatment more difficult and expensive in addition to causing taste and odor in drinking water.

With OWASA’s support, local governments have adopted limits on development in the University Lake and Cane Creek Reservoir watersheds because development is associated with higher rates of stormwater runoff which may carry pollutants and phosphorus and nitrogen compounds into lakes.

OWASA and other governments have also acquired land or conservation easements in selected areas to help keep land in natural condition to help protect water quality.

To help limit phosphorus and nitrogen in lakes and creeks, we encourage our customers to minimize their use of fertilizer and, when used, ensure it is properly applied.