What Causes Odors in Water

Posted February 18th, 2013

  Finding the Source of Foul Odors in Water and Getting Rid of It

 adapted from a February 2013 article in  Water Technology.


 Water News in a Nutshell

With the drought much of the U.S. has experienced during the last two years, odor related issues in water have become more severe. Odors can come from excess chlorine, from hydrogen sulfide, from improperly installed equipment–from a variety of causes. Common rotten egg odor usually called hydrogen sulfide can have a variety of causes.  Hot water heaters are often involved.Chlorine and hydrogen peroxide are often used to get rid of unwanted odors. Always read the manufacturer’s instructions and always call a professional if you ever smell something that doesn’t please you.


Smell is one of the five major senses we have and certainly one we use on a daily basis. Whether it’s the coffee we drink in the morning, the tempeh sandwich for lunch or the weird stench coming from the back of the car, we all use our sense of smell all the time. Some smells we like.  Others we don’t.

Finding the source

Often, a smell will come into a home or office unannounced and finding the cause of that smell is a frustrating task. If you find out the smell is coming from your water, the first thing you should do is contact the professionals or your local water utility board.Poor maintenance can be to blame for some foul odors. If a fixture was improperly installed, then it would be best to call the person who installed it to come and fix the problem.One water treatment expert lists improper maintenance as one of his two reasons for offensive odors in point-of-use (POU) drinking water systems, along with improper contaminant identification and subsequent improper pretreatment techniques.The foul odor associated with water is usually described as a rotten-egg smell. If you’ve ever experienced this problem with water or been around an actual rotten egg, then you probably know the smell.Hydrogen sulfide is normally pegged as the reason for a rotten-egg smell. Sometimes the hydrogen sulfide odor may only be present in the household’s hot water only. This indicates a problem with the water heater. 

The chlorine effect

But, say experts, the most common cause of odor in drinking water comes from chlorine. Chlorine is added by municipalities to disinfect water by killing bacteria and harmful viruses.“If your home uses water supplied by a public water treatment plant, the level of chlorine will be higher the closer you are to the treatment plant rather than a water user located several miles further away,” says one expert.

“The chlorine dissipates in the water lines and the treatment plant must ensure users the furthest away have an adequate chlorine level for disinfection. Also, at times the treatment plant may add higher levels than normal of chlorine due to maintenance or water related issues.”The disruption caused by the use of chlorine may be annoying and seem unpleasant to drink, but it is usually deemed safe by utility departments using this process.On occasion some municipal systems may experience a loss of chlorine residual which can result in a rapid increase in microbial activity. In the presence of sulfates accompanied by a loss of chlorine residual, nascent levels of sulfate reducing bacteria can grow exponentially and produce hydrogen sulfide gas from sulfates. Generally speaking, the higher the levels of combined sulfates and total organic carbon (TOC), the greater the potential for this occurrence.This becomes more of a problem during warm weather seasons. As the water heats up microbial activity increases, causing a foul odor smell.This phenomenon can occur either in the water mains, or more often it happens after the fact once the water has been dechlorinated by the point-of-entry (POE) or POU system.

Metallic odors may be due to the kind of piping used, while chemical odors may be due to flux used in soldering. Most of the time, the odors subside as water flows through the heater and over time.Lastly, another common cause of taste and odor issues comes from geosmin and 2-methylisoborneaol (MIB). These are naturally occurring compounds produced by blue-green (cyan bacteria), diatoms and actinomycetes.During the summer these organisms multiply in warm surface water, then die. The geosmin and MIB are then released into the water causing an odor, typically described as Earthy-musty.

These compounds do not affect human health, but can be detected by human senses at parts per trillion (ppt) levels.As you can see, there are many reasons why we experience odors in our water. Finding the source of that smell is very important, and usually something that should be done by a professional.

Dealing with foul odors

Now that we know some of the causes of water related odors, the next step is to figure out how to eliminate them. We talked to a couple different experts on the subject who offer varying views on how to treat foul odors.As mentioned above, good maintenance is the best way to reduce and prevent odors. This is especially true when dealing with hydrogen sulfide in a POU device. In this case, the first line of attack is proper maintenance.

Good maintenance is very simple and most often prescribed in detail by the manufacturer. Always refer to the manufacturer’s recommendations for maintenance.Other methods are frequent filter changes along with sanitizing the system. Properly sanitizing with sodium hypochlorite or hydrogen peroxide with help eliminate odors.Activated carbon is another solution to help reduce odors.

Remember, during the summertime municipalities increase their chlorine dosage so it’s important to replace the activated carbon in the spring time before it becomes over saturated with contaminants.Activated carbon systems excel at removing all of these odors. Granular activated carbon should be used for whole house point-of-entry systems, and carbon blocks or granular activated carbon for point-of-use systems. For hydrogen sulfide odor, a special surface-enhanced activated carbon is recommended.

Surface-enhanced activated carbons are specifically made to handle hydrogen sulfide odor more effectively than traditional activated carbons.That leads us back to the rotten-egg smell. Customers that are experiencing this issue can choose between temporary and more lasting treatment options.Peroxide is a temporary fix to rotten-egg odor in all situations, but the next time the heater sits idle, odor will return.

Chlorine bleach can also be used, but it is much more dangerous. The bacteria that cause the odor, otherwise harmless, are anaerobic, which means oxygen kills them. Both peroxide and bleach provide that oxygen. But, peroxide does not have to be flushed out of the system after use.Some odors are wrongfully blamed on the water heater. If a person has odor in one bathroom, but not another, then application of chlorine bleach to drains and sink overflows will probably make a difference.Another solution for rotten-egg odor issue is to remove the sacrificial anode, but this will void the warranty for every water heater made in the U.S. and it reduces its lifespan.

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