Taste and odor (T/O), at objectionable levels, occur in approximately 10-15 percent of water wells in New Hampshire. Hydrogen sulfide odor (rotten eggs) is reported most often.  For information on hydrogen sulfide please see the DES fact sheet WD-WSEB-3-16 entitled, "Hydrogen Sulfide in Drinking Water."  This fact sheet discusses T/O contaminants other than hydrogen sulfide.

In groundwater supplies, the origin of T/O contaminants generally cannot be determined.  The principal causes of T/O are thought to include:

In surface water, T/O problems typically are attributed to algae and dissolved organic matter.  T/O problems in surface water in New Hampshire are generally rare. The most common T/O by-products are 2-methylisoborneol and geosmin.  The DES laboratory does not test for either of these factors.  The DES strongly cautions against the use of unfiltered, undisinfected surface water for drinking purposes.

LABORATORY TESTING
The characterization of odor is often very difficult because T/O identification generally is very subjective.  The DES laboratory does not generally characterize odors in drinking water samples.  However, the laboratory can test for particular elements or compounds thought to cause a particular T/O condition.

If you desire to identify the compound(s) that are creating T/O you should recognize that this will be a difficult process with a low likelihood of success (other than for the compound   hydrogen sulfide).  First, you will need to decide what contaminant(s) are believed to cause the T/O.  Then have the laboratory test for that factor(s).  If that factor is present at elevated levels, then that factor probably contributes to the overall problem.  If it is not present at meaningful amounts, the hypothesis will need to be revised and laboratory tests processed for these new compounds.  Please see page 4 for some, but by no means all, T/O causing compounds.

MANMADE CAUSES
Occasionally, T/O can indicate the presence of serious health related contaminants such as those from industrial chemicals. These are often associated with land uses such as landfills and industrial areas. In years past, these chemicals were also associated with "mid-night dumping" in rural areas. To determine the presence of these contaminants, very expensive laboratory testing is typically required.  Whether there is sufficient justification for such testing would require an evaluation of the area nearby and uphill of your well.

HEALTH SIGNIFICANCE
Until the factor(s) creating the T/O is identified, an assessment of health significance of T/O can not be made.

When a well shows a noticeable and rapid change in T/O characteristics, after a long history (at least two-three years) of stable quality, the safety of the water source should be questioned and laboratory testing performed.  Some wells have seasonal variation in T/O characteristics. If occurring every year, these would likely imply a condition of natural origin with lower risk.

TREATMENT
T/O characteristics generally can be removed from drinking water.  The most common treatment options are listed below.

Aeration:  In this process, large volumes of air are blown through the water.  The T/O factors volatize into the air bubbles.  This air is vented to the outside of your home similar to the way moist, lint-laden air vents from a clothes dryer.

An important requirement of this method is the need to have clean air, free of dust, mosquitoes, etc.  The principal disadvantage of aeration is the possibility of creating bacterial growth in the treated water and the high cost of the aeration equipment.  See fact sheet WD-WSEB-2-23. Aeration is also beneficial in removing radon gas and carbon dioxide (CO₂ ).  CO₂ can make water acidic, thus dissolving lead and copper from your plumbing.  See fact sheet WD-WSEB-3-4.

Oxidation:  In this method, an oxygen-like chemical (such as oxygen, potassium permanganate, ozone or chlorine) is added to the water.  The oxygen-like chemical reacts with the odor compounds and is chemically destroyed.  One variation on this process uses a venturi nozzle to add small amounts of ordinary air to the water. Oxygen in the air reacts with the contaminants and the remaining air is removed from the water by an air relief valve. This system generally offers good service at low cost. 
Adsorption:  In this process, the raw water is passed through activated carbon.  The carbon can be granular or a 'pressed block.'  The T/O components adsorb (stick) to the interior surface of the carbon particles as the water passes through.  Activated carbon may not fully remove certain T/O factors.  Further, where radionuclides are high, adsorption of radon, uranium, radium and others radionuclides may create a low level radionuclide waste and/or a source of radiation within the home.

CHOOSING THE TREATMENT PROCESS
T/O treatment can be somewhat experimental. Typically one method will be tried to see if that method works for your particular T/O type. If not, another method from those above will be tried. Experienced water treatment professionals will know which option to try first.

Where the T/O characterization is unusual, a so-called 'pilot-size treatment process" could be tried.  This approach allows the treatability of the T/O to be determined easily on a small scale device before major effort and expense is committed to installing the full size treatment device.

Often the laboratory will not be able to identify any of the contaminant(s) which likely would cause T/O.  In such cases a treatment device, often activated carbon, will be installed at least at the kitchen sink with the hope of lowering the concentration of the unknown contaminant. In such situations the water is not necessarily thought of as pure, but the treatment is seen as improving an unacceptable poor situation.

T/O REFERENCES
Shown on the next page are common T/O characterizations and the contaminants that may cause them.  The principal reference for this list is:  Taste and Odor in Drinking Water,  American Water Works Research Foundation Report  ISN 0-89867-864-1, 1996

FOR ADDITIONAL INFORMATION
For more information concerning treatment, please refer to the DES fact sheet WD-WSEB-2-5 entitled, "Considerations When Purchasing Water Treatment Equipment."

For additional information, please call the DES Water Supply Engineering Bureau at 271-3139.  We would appreciate your comment concerning this fact sheet and your experiences relative to treatment of T/0. For an overall listing of water supply related fact sheets, please request fact sheet WD-WSEB-15-2.  Drinking water fact sheets are available through the DES web site at: www.des.state.nh.us/wseb  then select: fact sheets.  Please check the internet annually for updates of this document.   11/00