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Taste & Odor

Water picks up taste and odor from chemicals that dissolve easily because it is the "universal solvent." Water can pick up taste and odor from the chemical present in the air. For example, water stored in a refrigerator will eventually absorb the odor of pungent foods such as onion or garlic.


How do we perceive tastes or odors?

People differ in their ability to sense tastes or odors, and often describe identical sensations in different ways. Odors also affect our taste perceptions. This causes us to frequently describe tastes in terms of an associated odor. Our mouths also can detect physical sensations such as chalky or gritty, metallic, or astringent (dry).

Customers experiencing odor in their tap water often indicate that the odors are present only in their hot water. Heated water can intensify odor, just as cooking a soup makes the kitchen fill with the aroma. The source of an odor may be present in cold water, but the odor is not released until the water is heated.

The sense of smell can be confused by other factors. A person may describe water from a sink tap as smelling "septic." Moist, partially clogged drain traps or garbage disposals may be the actual source of the smell, rather than the tap itself. Decaying waste in the drains may smell "septic," causing water drawn at that location to seem to have the same odor.

What are some common sources of waterborne tastes or odors?

Algae occur naturally in lakes and streams. Some species produce chemicals which impart "earthy," "musty" or "moldy" odors to water. Decaying organic material, such as dead leaves or aquatic plants and algae, often cause "swampy," "grassy," "woody" or "septic" tastes or odors. Seasonal temperature changes in lakes and reservoirs may cause a turnover condition that can promote algal growth. Lake turnover is the mixing of layers of water which occurs naturally in late fall and early winter, as the top layers cool faster than the bottom. This may also bring decaying organic material into the treatment plant intake(s), where the treatment process reduces the organic content of the water to acceptable levels.

Untreated water can also be subject to agricultural or industrial run-off which may affect taste and odor. Water which contains these types of chemicals is usually described as having a "phenolic," "petroleum or hydrocarbon," or "plastic" odor. In communities with water sources downstream from major sources of such contaminants, the treatment process reduces raw water contents, but taste and odor may remain. Fortunately, Denver's water collection system has very little affect from such pollutants. Usually, our raw water contains very low levels of organics when it enters the treatment process.

The water treatment process itself uses and may create chemicals which can cause taste or odor. Disinfected water may retain a faint "bleachy" odor, for example. Water which resides in pipes for long periods of time through lack of use can develop a "stale" taste or odor. A "stale" water condition may occur in dead ends on the delivery system. Stale water conditions are more likely to occur in summer when higher temperatures cause the disinfectant (which remains in the water, at very low levels mandated by public health regulations) to dissipate more quickly.

Customers with "point of use" (in the home, typically) ion-exchange water softeners may notice a "salty" taste to their water. This comes from the salt used to "exchange" minerals that cause hardness. Home water conditioning systems can be the source of various disagreeable tastes or odors. Carbon filters, for example, should be exchanged as indicated in the user manual because they can serve as a medium for bacterial growth.

Unpleasant tastes or odors in drinking water may indicate unsafe plumbing conditions called cross-connections. A cross connection is a physical connection between a potable (drinkable) water supply and a source of contamination or pollution.

Are the chemicals which cause tastes or odors harmful to human health?

Synthetic chemicals such as hydrocarbons that have been proven to present a health risk are regulated under federal and state rules. However, these synthetic chemicals are not present in the Denver Water system in problem concentrations. Naturally occurring chemicals (organic compounds) which cause disagreeable taste and odor can be present depending on a variety of conditions, such as the weather, but they do not pose health risks.

The "bleachy" smell of some clear water signals the presence of disinfectant, which is a necessary part, in low concentrations, of making water safe to drink. The Centers for Disease Control have identified disinfection of drinking water as one of the most significant health advances in history, virtually halting the epidemic occurrence of deadly diseases like typhoid and cholera. On the one hand, state or federal regulations mandate the presence of disinfectant in treated water and on the other, regulations also set strict limits on the concentration levels of both the disinfectants and their byproducts. Denver's drinking water meets all water safety and health regulations, including these.

Some tastes and odors are of concern. "Stale" tasting water can indicate a lack of disinfectant. Cross-connections are potentially hazardous sources of contamination that may cause unpleasant odors. For example, a hose in a floor drain may siphon the drain's contents into potable water.

What is Denver Water doing to minimize or eliminate the presence of taste and odor causing chemicals?

The incidence of both naturally occurring and synthetic chemicals in our raw water is minimized through careful management of Denver's water sources and watershed. Denver Water operates its treatment plants so they reduce concentrations of compounds that affect taste and odor. Denver Water replaces or repairs water mains which are in poor operating condition. Water mains are flushed periodically, especially in dead-end locations, to replace stale water with fresh water.

Our system is monitored carefully to maintain high levels of quality. Customers also are an excellent source of information about local water conditions. If you have a concern about your water quality, call 303-893-2444 to resolve the problem. Quality problems may be caused by on-site plumbing conditions beyond our jurisdiction, and if so, it may be determined that you need the services of a plumber. Every customer inquiry is taken seriously and investigated to an appropriate resolution.