There is no odor so bad as that which arises from goodness tainted.
Henry David Thoreau
From its perch high in the clouds all the way down to our faucets, as water makes its journey down to earth it is sure to come into contact with a variety of substances including gases, minerals, and a whole host of organic materials. With this in mind, you can pretty well bet that it will pick up at least a few impurities along the way. While some of these impurities are completely dissolved, others are not and can often cause objectionable color, taste, and yes, even odor.
Since taste and odors can serve as a warning sign that a harmful substance (herbicides, pesticides, sewage, etc.) has made its way into your water supply, system operators and decision makers need to be familiar with how to detect, identify, and control taste and odor problems that effect their final product. Plus, as any water operator who isn't still "wet-behind-the-ears" knows all too well, taste and odor problems are most often the customer's number one complaint.
While there are any number of ways to deal with less-than-tasty and odorous contaminants, such as, keeping them out of the water, removing them from the water, or simply destroying them in the water, it's important that systems take every possible step to quickly address odor and taste issues as they arise.
Remember: If it looks like tea...smells like corn...and tastes like cucumbers...then the chances are that it shouldn't be coming out of your faucet.
In this issue of the Safe Drinking Water Trust eBulletin we'll take a look at what your system can, and just might be required, to do when your customer's start to make a stink about the water they drink.
Additional Resources
Tacoma Water Utility’s Answers to Common Questions
www.ci.tacoma.wa.us/water/WaterQuality/solutions.htm [1]
When Seconds Count
Years ago the good folks over at the U.S. Environmental Protection Agency established the National Primary Drinking Water Regulations. These requirements set mandatory water quality standards for drinking water contaminants. The rule set enforceable standards called "Maximum Contaminant Levels" (MCLs) and were established to protect the public against consumption of drinking water contaminants that present a risk to human health. An MCL is the maxim allowable amount of a given contaminant in drinking water which is delivered to the consumer.
In addition to the Primary Drinking Water Regulations, the EPA has also established the National Secondary Drinking Water Regulations. These are non-mandatory water quality standards for 15 additional contaminants. It is into this category that many of the standard odor and taste altering contaminants fall, since they generally don't present a risk to human health at low levels. While the EPA does not enforce these "Secondary Maximum Contaminant Levels" (SMCLs), they do serve as guidelines for water systems and can be used to manage drinking water for aesthetic considerations, such as taste, color, and odor.
Tip: Be sure to check out the EPA's National Primary Drinking Water Regulations and National Secondary Drinking Water Regulations webpage for a complete list of MCLs and SMCLs at: www.epa.gov/safewater/mcl.html [2]
Surface water supplies are generally the most susceptible to substances causing undesirable taste and odor issues. And in most cases, it is inorganic compounds (non-living such as sodium chloride, ferric hydroxide, aluminum sulfate, etc.) that lead to unwanted taste problems. However, the most significant source of odor causing problems in drinking water sources are organic (living) compounds such as the growth and decay of microorganisms or algae that are most often at the root of odor complaints.
Additional Resources
Virginia Tech's Drinking Water Treatment Primer on Odor and Smell
ewr.cee.vt.edu/environmental/teach/wtprimer/taste2/frontpg3.html [3]
The Taste Test...We Let You Decide
Taste and odor can be classified as aesthetic (relating to the senses) qualities of drinking water, meaning that their measure depends on human perception (taste, smell, appearance, etc.), making them difficult to measure. Some of the more typical complaints that customers report coming from their water are:
•Sewer Smell
•Chlorine Smell
•Chlorine Smell and Taste
•Rotten Egg Smell
•Petroleum Smell and Taste
•Metallic Smell and Taste
•Earthy or Fishy Smell and Tastes
When evaluating water samples for taste and odor problems, two of the most commonly used tests are the Threshold Odor Test and the Flavor Profile Analysis. However, in many cases, additional testing such as pH, dissolved oxygen, nutrient loading, and other tests gauging the physical aspects of the water will also be required to determine the cause of the problem.
A Threshold Odor Test can be performed for a number of reasons. Often it is used to quantify the strength of odor given by chlorine in finished drinking water. However, it can also be applied to raw water and algal odor problems. Generally the testing process is conducted by a panel of examiners with the averaged outcome indicating the relative strength of the odor in the given water sample. It is always important to remember that Threshold Odor Testing is not an exact science since there are clearly differences in every person's olfactory (smelling) ability.
During testing, the actual measurement of the odor level is referred to as a TON (Threshold Odor Number). A TON is defined as the greatest dilution of the sample with odor-free water yielding a perceptible odor.
Conducting a Flavor Profile Analysis (much like the good ol' Pepsi Challenge) can also be tricky since the "taste" of water is actually the result of many sensory perceptions coming together all at one time. Depending on the chemical substances present, taste, odors, and mouth-feel all add up to what is generally referred to as the water's "flavor."
Tip: Flavor Profile Analysis should only be performed on water that is safe for ingestion!
During a Flavor Profile Analysis, a panel of trained tasters attempt to detect contaminants at various dilutions and define the nature of the taste (and any odor) either in their own words or through the use of standard descriptions. In most cases, the all too standard definition of "tastes like chicken" has been eliminated from the list of standard descriptions.
In order to remove the "human element" in this type of testing, some labs are moving toward the use of "mechanical sniffers," which operate much like a human nose yet require fewer Kleenex.
Additional Resources
Guide for Odor and Taste Assessment Analysis
www.mcguireinc.com/papers/RM_AWWA_self%20assessment.pdf [4]
In the Nose of the Beholder
Overcoming taste and odor problems can often be accomplished through several simple and inexpensive routine treatment methods.
Chlorinous, Bleachy, Chemical, or Medicinal Tastes and Odors
There are generally two common causes for a chlorinous, bleachy, chemical, or medicinal taste or odor in drinking water:
• The addition of chlorine to the water supply by the water system
(if the water has a chlorine smell, but no chlorine taste, it is possible that the water needs more chlorine)
• The interaction of chlorine with a build-up of organic material in a distribution system
Chlorine is the most widely used disinfectant applied to potable water supplies today. To address this issue, operators can use a chlorine field test kit to determine if the complaint stems from total of free chlorine residuals. If the free chlorine residual is zero or substantially less than the total chlorine residual, then there has likely been a demand for the chlorine somewhere in the distribution system. To increase the free chlorine residual, flushing the distribution system near the complaintant's house should work, If not, then it might be a good idea to increase the chlorine dosage at the nearest chlorine feeder.
Remember, during the summer months when the temperatures rise, chlorine dissipates faster and most systems tend to chlorinate more to make up for the demand.
Rotten Egg, Decayed, or Sewage-like Taste or Odor
There are generally three common causes of a sulfurous, decayed, or sewage-like taste or odor in drinking water:
• Algae growth
• Increased levels of hydrogen sulfide (H2S)
• Possible sewage contamination
If the complaint is related to a rotten egg like odor coming from a groundwater system, then the problem is possibly related to increased levels of hydrogen sulfide. The best way to treat this problem is to aerate the water. This can be done either mechanically or by chemical means, giving the hydrogen sulfide an opportunity to release. Other treatment methods include carbon filtration, ion exchange, and oxidizing filters.
The greatest chance for taste and odor problems related to algae to occur are when an algal bloom occurs (a sudden or rapid growth of the algae). This typically happens during the summer months due to excessive sunlight. However, this can also occur in reservoirs or ponds when nutrient loading is high. There are several ways to address algal taste and odors problems. One is nutrient limitation, whereby the main nutrients, nitrogen and phosphorous levels are limited in the reservoir. Another method is the removal of the tastes and odors during treatment, and a third is to control the algae through chemical applications.
Additional Resources
The National Environmental Services Center's Tech Brief: Taste and Odor Control
www.nesc.wvu.edu/ndwc/articles/OT/SP06/OTsp06_TB.pdf [5]
Other Methods of Taste and Odor Reduction
Since most taste and odor causing compounds exist in a reduced form, oxidation is generally considered to be an effective means of removal. The most commonly used compounds for completing this process include chlorine, permanganate, ozone, and chlorine dioxide. Chlorine has been found to be very effective in removing low-level inorganic odors such as hydrogen sulfide.
The use of potassium permanganate is also useful in treating industrial and algal odors. Ozone is another excellent oxidizing agent for taste and odor problems, although it often requires high doses to remove some odors. As a result, it is mainly used to reduce natural aquatic odors. Chlorine dioxide is also successfully used by many systems to control algae and other odors.
Many systems also rely heavily on aeration to handle more easily removed substances such as sulfides.
And last, but certenally not least, many systems turn to activated carbon absorption as a reliable method of removing taste and odor from their drinking water sources. Activated Carbon can be used in two forms, powered activated carbon or granular activated carbon. In the past, activated carbon in its powered form was primarily relied on to remove common taste and odor problems. However increased industrial compounds now often require its use in the granular form.
Whatever treatment method your system selects to use for the treatment of odor and taste problems, it is important that all methods be approved by the proper regulatory authorities, so that your relationship with both your state primacy agency and your customer's doesn’t turn sour.