Water Well Journal
Issue link: http://read.dmtmag.com/i/498253
A s opposed to water quality issues involving regulatory elements or compounds or even non-regulated aesthetic problems such as iron, manganese, or calcium hard- ness, problems with taste and odor in drinking water are usually difficult to ascertain and often require extensive testing. Included in this type of identification process are unusual tests such as subjec- tive taste and odor test panels consisting of typical water consumers. This month, we'll examine the problems associated with taste and odor in water supplies and the various methods used to identify and treat them. Review of Water Analysis Results The results from past and recent water quality analysis tests are initially examined to determine any potential contaminants that may contribute to taste and odor problems as well as ver- ify the lack of any contaminants—such as many inorganics, organics, and phe- nols—that could pose health hazards to individuals who may consume the water. In order to verify this, a full water analysis for inorganic (heavy metals), volatile and synthetic organics, and sec- ondary contaminants in the water that are known to cause or impact a taste and odor problem is generally warranted. Field tests for hydrogen sulfide, methane, ammonia, and other dissolved gases at the wellhead are usually needed too. Causes of Taste and Odor Complaints in Drinking Water Undesirable tastes and odors in drinking water are normally a result of a combination of factors. The materials contributing to these problems can come from many sources, including those found in nature as well as many that are man-made. Problems related to taste and odor in water do not usually present any partic- ular health hazard. However, people are naturally concerned the water they drink be at least palatable, and if possible, pleasant-tasting. One of the most common complaints related to taste or odor of drinking water is related to the use of chlorine as a dis- infecting agent or oxidant. Often, it is referred to as a "chlorine taste." Chlo- rine is noticeable and sometimes offen- sive to some individuals at levels as low as .20 to .30 mg/L, which also happens to be a typical residual value. In some cases, particularly with fil- tered surface water supplies that use coagulants or polymers for water treatment, taste or odors can result from the interaction of the water treatment chemical to organic constituents in the raw water. This can be particularly true for surface waters with high levels of algae, bio-growth, or certain organic acids like tannin or humic acid. In many instances, changing the dosage rate of the chemical or even changing the chemical altogether will correct the problem. Generally, surface water sources are more commonly linked to taste and odor problems than are groundwater supplies. This is mostly due to the presence of algae, bacteria, and decayed vegetation. Most tastes and odors in groundwater supplies are caused by bacterial actions within the groundwater aquifers or the wellbore or the dissolution of salts and minerals as groundwater percolates and flows through geologic deposits. Intrusion of salt or mineralized water may also cause taste or odor problems. Dissolved gases such as hydrogen sul- fide, ammonia, and methane may also exist which will separate from a water solution at atmospheric pressure or upon heating, causing odor problems. Hydrogen sulfide is characterized as a swampy, musty odor at low concentra- tions of even less than .10 mg/L, or when present at higher concentrations— observed as a rotten-egg odor. It is at- tributed to anaerobic bacterial action on organic sulfur, elemental sulfur, sulfates, or sulfites. High salt content, as indicated by total dissolved solids or conductivity, can result in taste problems but does not usually result in odor complaints. Situations primarily due to human activity resulting in tastes and odors in groundwater occur as a result of chemi- cal dumping, landfill disposal, leachate runoff, or industrial waste disposal. Analysis of water for synthetic organic chemicals is used to eliminate this possibility. Iron and manganese may also impart taste problems, notably resulting in a taste described as "metallic," or "like iron," or "rusty" but in low concentra- tions usually doesn't cause odor com- plaints. An exception is with off-gassing that occurs in situations with iron-using bacteria in groundwater wells. All the above noted causes are possible in both groundwater and surface water supplies. ED BUTTS, PE, CPI ENGINEERING YOUR BUSINESS TASTE AND ODOR IN DRINKING WATER Know the ways to combat the pesky problems of bad tasting or foul smelling water. Bad taste and odor in drinking water is always a highly subjective characteristic of the water's quality and often difficult to correct to everyone's satisfaction. waterwelljournal.com 54 May 2015 WWJ