Drinking Water Taste and Odor

Health concerns are not the only criteria that we use to judge our drinking water. In fact, often the most noticeable qualities that determine whether water is acceptable to consumers are unpleasant taste or odor, staining, poor reaction with soap, or mineral buildup in pipes and plumbing. These problems result from elevated concentrations of "nuisance" constituents.

Most nuisance constituents occur naturally. These constituents are more likely to occur at nuisance concentrations in groundwater than surface water, because they result from the reaction of groundwater with aquifer rocks and sediments as the water moves underground. Dissolved iron in groundwater can stain laundry, sinks, bathtubs, and toilets a brownish red, and can degrade plumbing and heating systems. Iron also gives drinking water an unpleasant taste, making it undrinkable for many well owners. Manganese often co-occurs with iron and causes many of the same problems. Hard water—defined by high concentrations of calcium and magnesium—causes water pipes and fixtures to become coated with scale, limits the ability of soaps and detergents to form suds, and can cause premature failure of plumbing and heating fixtures.  pH outside of acceptable ranges can give water a metallic taste and can cause corrosion of pipes. A high dissolved solids concentration—a measure of all dissolved substances in water, also referred to as salinity—makes water taste disagreeably salty. Find a table that lists nuisance constituents and their noticeable effects at high concentrations here.

EPA Guidelines for Nuisance Constituents
The EPA recommends limits, called Secondary Maximum Contaminant Levels (SMCLs), for nuisance constituents in public water supplies. The SMCLs are non-health-based, non-enforceable guidelines for concentrations of 15 constituents in drinking water. These guidelines are designed to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color, and odor. These contaminants are not considered to present a risk to human health at the SMCL.

Because they can be smelled, tasted, or seen, nuisance constituents may be more likely to be noticed by consumers than contaminants that actually are a health risk. However, some constituents that have an SMCL also have a higher human-health benchmark. Manganese is one example—the black staining caused by manganese might be just a nuisance or might signal a concentration high enough to be a health risk. In other situations, the presence of nuisance constituents can signal geochemical conditions that promote high concentrations of other, more harmful contaminants.  For example, high concentrations of dissolved solids are considered a nuisance because they cause water to taste salty, but high dissolved solids is not in itself a health concern. However, high dissolved solids can be an indication that there are elevated concentrations of arsenic, uranium, or other trace elements in the groundwater as well. The occurrence of nuisance constituents in drinking water therefore can indicate that testing for a broader range of constituents could be warranted to assess possible risks and to determine options for reducing those risks.

Nuisance Constituents in Groundwater Used for Drinking
Because the constituents considered to be a nuisance at high levels occur naturally in groundwater, it can be very common for drinking water from wells to have nuisance constituents. In a recent survey of 11 Principal Aquifers that supply most of the groundwater used in the U.S., groundwater contained at least one constituent at a concentration above its SMCL in 15 to 65 percent of the area studied in each aquifer.  And in a survey from 1991 to 2010 of wells across the U.S. that tap the parts of aquifers used for drinking, at least one nuisance constituent exceeded its SMCL in more than half of the wells sampled. Nuisance constituents were particularly prevalent in the Glacial aquifer system (northern U.S.) and the Cambrian Ordovician aquifer system (north-central U.S.), where groundwater in more than 60 percent of each study area contained at least one nuisance constituent above its SMCL.

Many of the geochemical processes that affect groundwater quality occur over a long period of time as the groundwater slowly moves through the aquifer. The older the groundwater, the longer the water has been in contact with aquifer materials, and the greater the degree to which geochemical processes can change the pH, dissolved oxygen content, and concentration of dissolved solids, thereby increasing the potential for elevated concentrations of some nuisance constituents.

Even if an aquifer provides a plentiful supply of potable groundwater, nuisance constituents can prevent many consumers from using it for drinking. Some consumers choose to buy bottled water rather than drink tap water, at a cost of hundreds of dollars each year. Water-treatment systems can remove nuisance constituents from groundwater but can be costly to install and maintain.