The incidence of “rotten egg” sulfur odors and often the resulting black water in hot and cold
water lines is due to the reaction of sulfates and microorganisms in water. This can occur in
the well directly, or in the household plumbing both hot and cold water pipes, or in only the
water heater and hot water lines.
HYDROGEN SULFIDE AND SULFUR BACTERIA IN WELL WATER
Hydrogen sulfide gas (H2S) can occur in well water, and gives the water a characteristic
"rotten egg" taste or odor. This information is provided to help explain the cause of the
problem and to give the reader some solutions to reduce or eliminate the problem.
What are the sources of hydrogen sulfide in well water and the water distribution
system?
Hydrogen sulfide gas can result from a number of different sources. It can occur naturally in
groundwater. It can be produced by certain "sulfur bacteria" in the groundwater, in the well,
or in the water distribution system. It can be produced also by sulfur bacteria or chemical
reactions inside water heaters. In rare instances, it can result from pollution. The source of
the gas is important when considering treatment options.
Are sulfur bacteria or hydrogen sulfide harmful?
In most cases, the rotten egg smell does not relate to the sanitary quality of the water.
However, in rare instances the gas may result from sewage or other pollution. It is a good
idea to have the well tested for the standard sanitary tests of coliform bacteria and nitrate.
Sulfur bacteria are not harmful, but hydrogen sulfide gas in the air can be hazardous at high
levels. It is important to take steps to remove the gas from the water, or vent the gas to the
atmosphere so that it will not collect in low-lying spaces, such as well pits, basements, or
enclosed spaces, such as well houses. Only qualified people who have received special
training and use proper safety procedures should enter a well pit or other enclosed space
where hydrogen sulfide gas may be present.
Are there other problems associated with sulfur bacteria or hydrogen sulfide?
Yes. Sulfur bacteria produce a slime and can promote the growth of other bacteria, such as
iron bacteria. The slime can clog wells, plumbing, and irrigation systems. Bacterial slime
may be white, grey, black or reddish brown if associated with iron bacteria. Hydrogen sulfide
gas in water can cause black stains on silverware and plumbing fixtures. It can also corrode
pipes and other metal components of the water distribution system.
What causes hydrogen sulfide gas to form in groundwater?
Decay of organic matter such as vegetation, or chemical reactions with some sulfur-
containing minerals in the soil and rock, may naturally create hydrogen sulfide in gas in
groundwater. As groundwater moves through soil and rock formations containing minerals
of sulfate, some of these minerals dissolve in the water. A unique group of bacteria, called
"sulfur bacteria" or "sulfate-reducing bacteria" can change sulfate and other sulfur
containing compounds, including natural organic materials, to hydrogen sulfide gas.
How is hydrogen sulfide gas produced in a water heater?
A water heater can provide an ideal environment for the conversion of sulfate to hydrogen
sulfide gas. The water heater can produce hydrogen sulfide gas in two ways - creating a
warm environment where sulfur bacteria can live, and sustaining a reaction between sulfate
in the water and the water heater anode. A water heater usually contains a metal rod called
an "anode," which is installed to reduce corrosion of the water heater tank. The anode is
usually made of magnesium metal, which can supply electrons that aid in the conversion of
sulfate to hydrogen sulfide gas. The anode is 1/2 to 3/4 inches in diameter and 30 to 40
inches long.
How can I find the source of a hydrogen sulfide problem, and what can I do to
eliminate it?
The odor of hydrogen sulfide gas can be detected in water at a very low level. Smell the
water coming out of the hot and cold water faucets. Determine which faucets have the
odor. The "rotten egg" smell will often be more noticeable from the hot water because more
of the gas is vaporized. Your sense of smell becomes dulled quickly, so the best time to
check is after you have been away from your home for a few hours. You can also have the
water tested for hydrogen sulfide, sulfate, sulfur bacteria, and iron bacteria at an
environmental testing laboratory. The cost of testing for hydrogen sulfide ranges from $20
to $50 depending on the type of test.
If the smell is only from the hot water faucet the problem is likely to be in the water
heater.
If the smell is in both the hot and cold faucets, but only from the water treated by a water
softener and not in the untreated water the problem is likely to be sulfur bacteria in the water
softener. If the smell is strong when the water in both the hot and cold faucets is first turned
on, and it diminishes or goes away after the water has run, or if the smell varies through time
the problems is likely to be sulfur bacteria in the well or distribution system. If the smell is
strong when the water in both the hot and cold faucets is first turned on and is more or less
constant and persists with use the problem is likely to be hydrogen sulfide gas in the
groundwater.
What can I do about a problem water heater?
Unless you are very familiar with the operation and maintenance of the water heater, you
should contact a water system professional, such as a plumber, to do the work. Precautions
must be made to make sure the water heater is turned off so the elements or the burner will
not turn on during any of these procedures. Also, the water is very hot and precautions must
be made not to burn yourself or others that may be there observing or helping!
What if sulfur bacteria are present in the well, the water distribution system, or the
water softener?
Have the well and distribution system disinfected by flushing with a strong chlorine solution
(shock chlorination). Sulfur bacteria can be difficult to remove once established in a well.
Physical scrubbing of the well casing, use of special treatment chemicals, and agitation of
the water may be necessary prior to chlorination to remove the bacteria, particularly if they
are associated with another type of bacteria known as "iron bacteria". Contact a licensed
well contractor or a well specialist for details. No attempt should be made by the home owner
to attempt such type of disinfection. Wells can be contaminated very easily and this type of
work must be performed by a licensed professional.
If the bacteria are in water treatment devices, such as a water softener, contact the
manufacturer, the installer on the procedure for disinfecting the treatment devices.
What if hydrogen sulfide gas is in the groundwater?
The problem may only be eliminated by drilling a well into different formation capable of
producing water that is free of hydrogen sulfide gas or connecting to an alternate water
source, if available.
However, there are several options available for treatment of water with hydrogen
sulfide gas.
water lines is due to the reaction of sulfates and microorganisms in water. This can occur in
the well directly, or in the household plumbing both hot and cold water pipes, or in only the
water heater and hot water lines.
HYDROGEN SULFIDE AND SULFUR BACTERIA IN WELL WATER
Hydrogen sulfide gas (H2S) can occur in well water, and gives the water a characteristic
"rotten egg" taste or odor. This information is provided to help explain the cause of the
problem and to give the reader some solutions to reduce or eliminate the problem.
What are the sources of hydrogen sulfide in well water and the water distribution
system?
Hydrogen sulfide gas can result from a number of different sources. It can occur naturally in
groundwater. It can be produced by certain "sulfur bacteria" in the groundwater, in the well,
or in the water distribution system. It can be produced also by sulfur bacteria or chemical
reactions inside water heaters. In rare instances, it can result from pollution. The source of
the gas is important when considering treatment options.
Are sulfur bacteria or hydrogen sulfide harmful?
In most cases, the rotten egg smell does not relate to the sanitary quality of the water.
However, in rare instances the gas may result from sewage or other pollution. It is a good
idea to have the well tested for the standard sanitary tests of coliform bacteria and nitrate.
Sulfur bacteria are not harmful, but hydrogen sulfide gas in the air can be hazardous at high
levels. It is important to take steps to remove the gas from the water, or vent the gas to the
atmosphere so that it will not collect in low-lying spaces, such as well pits, basements, or
enclosed spaces, such as well houses. Only qualified people who have received special
training and use proper safety procedures should enter a well pit or other enclosed space
where hydrogen sulfide gas may be present.
Are there other problems associated with sulfur bacteria or hydrogen sulfide?
Yes. Sulfur bacteria produce a slime and can promote the growth of other bacteria, such as
iron bacteria. The slime can clog wells, plumbing, and irrigation systems. Bacterial slime
may be white, grey, black or reddish brown if associated with iron bacteria. Hydrogen sulfide
gas in water can cause black stains on silverware and plumbing fixtures. It can also corrode
pipes and other metal components of the water distribution system.
What causes hydrogen sulfide gas to form in groundwater?
Decay of organic matter such as vegetation, or chemical reactions with some sulfur-
containing minerals in the soil and rock, may naturally create hydrogen sulfide in gas in
groundwater. As groundwater moves through soil and rock formations containing minerals
of sulfate, some of these minerals dissolve in the water. A unique group of bacteria, called
"sulfur bacteria" or "sulfate-reducing bacteria" can change sulfate and other sulfur
containing compounds, including natural organic materials, to hydrogen sulfide gas.
How is hydrogen sulfide gas produced in a water heater?
A water heater can provide an ideal environment for the conversion of sulfate to hydrogen
sulfide gas. The water heater can produce hydrogen sulfide gas in two ways - creating a
warm environment where sulfur bacteria can live, and sustaining a reaction between sulfate
in the water and the water heater anode. A water heater usually contains a metal rod called
an "anode," which is installed to reduce corrosion of the water heater tank. The anode is
usually made of magnesium metal, which can supply electrons that aid in the conversion of
sulfate to hydrogen sulfide gas. The anode is 1/2 to 3/4 inches in diameter and 30 to 40
inches long.
How can I find the source of a hydrogen sulfide problem, and what can I do to
eliminate it?
The odor of hydrogen sulfide gas can be detected in water at a very low level. Smell the
water coming out of the hot and cold water faucets. Determine which faucets have the
odor. The "rotten egg" smell will often be more noticeable from the hot water because more
of the gas is vaporized. Your sense of smell becomes dulled quickly, so the best time to
check is after you have been away from your home for a few hours. You can also have the
water tested for hydrogen sulfide, sulfate, sulfur bacteria, and iron bacteria at an
environmental testing laboratory. The cost of testing for hydrogen sulfide ranges from $20
to $50 depending on the type of test.
If the smell is only from the hot water faucet the problem is likely to be in the water
heater.
If the smell is in both the hot and cold faucets, but only from the water treated by a water
softener and not in the untreated water the problem is likely to be sulfur bacteria in the water
softener. If the smell is strong when the water in both the hot and cold faucets is first turned
on, and it diminishes or goes away after the water has run, or if the smell varies through time
the problems is likely to be sulfur bacteria in the well or distribution system. If the smell is
strong when the water in both the hot and cold faucets is first turned on and is more or less
constant and persists with use the problem is likely to be hydrogen sulfide gas in the
groundwater.
What can I do about a problem water heater?
Unless you are very familiar with the operation and maintenance of the water heater, you
should contact a water system professional, such as a plumber, to do the work. Precautions
must be made to make sure the water heater is turned off so the elements or the burner will
not turn on during any of these procedures. Also, the water is very hot and precautions must
be made not to burn yourself or others that may be there observing or helping!
- Disinfect and flush the water heater with a chlorine bleach solution. Chlorination can
kill sulfur bacteria, if done properly. If all bacteria are not destroyed by chlorination,
the problem may return within a few weeks. Add one cup bleach for every 5 gallons of
water the water heater holds. For example, a typical 40 gallon water heater would
require 8 cups of bleach. - Increase the water heater temperature to 160 degrees Fahrenheit (71 degrees
Celsius) for several hours. This will destroy the sulfur bacteria. Flushing to remove
the dead bacteria after treatment should control the odor problem.
- CAUTION: Increasing the water heater temperature can be dangerous.
Before proceeding, consult with the manufacturer or dealer regarding an
operable pressure relief valve, and for other recommendations. Be sure to
lower the thermostat setting and make certain the water temperature is reduced
following treatment to prevent injury from scalding hot water and to avoid high
energy costs.
- Replace or remove the magnesium anode. Many water heaters have a magnesium
anode, which is attached to a plug located on top of the water heater. It can be
removed by turning off the water, releasing the pressure from the water heater, and
unscrewing the plug. Be sure to plug the hole. Removal of the anode, however, may
significantly decrease the life of the water heater. You may wish to consult with a
reputable water heater dealer to determine if a replacement anode made of a
different material, such as aluminum or zinc, can be installed. A replacement anode
may provide corrosion protection without contributing to the production of hydrogen
sulfide gas.
What if sulfur bacteria are present in the well, the water distribution system, or the
water softener?
Have the well and distribution system disinfected by flushing with a strong chlorine solution
(shock chlorination). Sulfur bacteria can be difficult to remove once established in a well.
Physical scrubbing of the well casing, use of special treatment chemicals, and agitation of
the water may be necessary prior to chlorination to remove the bacteria, particularly if they
are associated with another type of bacteria known as "iron bacteria". Contact a licensed
well contractor or a well specialist for details. No attempt should be made by the home owner
to attempt such type of disinfection. Wells can be contaminated very easily and this type of
work must be performed by a licensed professional.
If the bacteria are in water treatment devices, such as a water softener, contact the
manufacturer, the installer on the procedure for disinfecting the treatment devices.
What if hydrogen sulfide gas is in the groundwater?
The problem may only be eliminated by drilling a well into different formation capable of
producing water that is free of hydrogen sulfide gas or connecting to an alternate water
source, if available.
However, there are several options available for treatment of water with hydrogen
sulfide gas.
- Install an activated carbon filter. This option is only effective for low hydrogen
sulfide levels, usually less than 1 milligram per liter (mg/L).* The gas is trapped by the
carbon filter is saturated. Since the carbon filter can remove substances in addition
to hydrogen sulfide gas, it is difficult to predict its service life. Some large carbon
filters have been known to last for years, while some small filters may last for only
weeks or even days.
- Install an oxidizing filter, such as a "manganese greensand" filter. This option is
effective for hydrogen sulfide levels up to about 6 mg/L. Manganese greensand
filters are often used to treat iron problems in water. The device consists of
manganese greensand media, which is sand coated with manganese dioxide. The
hydrogen sulfide gas in the water is changed to tiny particles of sulfur as it passes
through the filter. The filter must be periodically regenerated, using potassium
permanganate, before the capacity of the greensand is exhausted.
- Install an oxidation-filtration system. This option is effective for hydrogen sulfide
levels up to and exceeding 6 mg/L. These systems utilize a chemical feed pump to
inject an oxidizing chemical, such as chlorine, into the water supply line prior to a
storage or mixing tank. When sufficient contact time is allowed, the oxidizing chemical
changes the hydrogen sulfide to sulfur, which is then removed by a particulate filter,
such as a manganese greensand filter. Excess chlorine can be removed by activated
carbon filtration.
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Greg Liebig, CIAQT
Certified Home Inspector
B.S. Mechanical Engineering
WI License #1955-106
Certified Home Inspector
B.S. Mechanical Engineering
WI License #1955-106
| Updated: 1/21/08 |
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We hope you've found this article helpful! If you have any questions or comments,
please fill out our Contact Us Form or give us a call at (920) 451-4646. We would be
happy to serve you!
please fill out our Contact Us Form or give us a call at (920) 451-4646. We would be
happy to serve you!