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Rotten Egg Odor In Water
Why
Does My Water Smell Like Rotten Eggs?
Hydrogen
Sulfide and Sulfur Bacteria in Well Water
Well
Management Program
Minnesota
Department of Health
Hydrogen sulfide gas
(H2S) can give water a “rotten egg” taste or odor. This gas can occur in wells
anywhere and be:
- Naturally occurring - a result of decay and
chemical reactions with soil and rocks.
- Produced by certain “sulfur bacteria” in the
groundwater, well, or plumbing system.
- Produced by sulfur bacteria or chemical
reactions inside of water heaters.
- From pollution (this is rare).
May Help Other
Bacteria Grow
Sulfur bacteria
produce a slime and can help other bacteria grow, such as iron bacteria. The
slime can clog wells, plumbing, and irrigation systems.
Gas May be Harmful
While sulfur bacteria
are not harmful, hydrogen sulfide gas in the air can be harmful at high levels.
It is important to
remove the gas from the water, or vent the gas to the atmosphere.
Venting prevents the
gas from collecting in low-lying spaces (such as well pits and basements) or
enclosed spaces (such as well houses).
Only well
professionals should enter a well pit or other enclosed space where hydrogen
sulfide gas may be present.
How to Detect
Bacterial slime may
be white, grey, black, or reddish brown if associated with iron bacteria (signs
of sulfur bacteria).
Black stains on
silverware and plumbing fixtures (signs of hydrogen sulfide gas).
Corrosion on pipes
and metal components of the water distribution system (signs of hydrogen
sulfide gas).
Have your water
tested at a laboratory.
Consider Testing Your
Water
In rare instances,
the gas may be from sewage or other pollution. To be safe, test your well water
for coliform bacteria and nitrate.
What You Can Do
The first step is to
find out what the source of the issue is; that will let you know what treatment
option is best.
How to Find the
Source
After you have been
away from your home for a few hours, smell the water coming out of the hot and
cold water faucets. Determine which faucets have the “rotten egg” odor.
Flow chart decision
tree. Is there a smell from the cold water faucet? If no, the problem is likely
in the water heater.
If yes, is there a
smell from faucets not connected to the water softener? If no, the problem is
likely sulfur bacteria in the water softener.
If yes, is the smell
less noticeable after the water runs for a few minutes? If no, the problem is
likely hydrogen sulfide gas in the groundwater. If yes, the problem is likely
sulfur bacteria in the well or plumbing system.
If the Problem is in
the Water Heater
Unless you are very
familiar with water heater operation and maintenance, have a plumber or water
system professional to do the work.
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 water heater dealer to determine if a replacement anode made of
a different material, such as aluminum, can be installed.
A replacement anode
may provide corrosion protection without contributing to the production of
hydrogen sulfide gas.
Disinfect and flush
the water heater with a chlorine bleach solution. Chlorination can kill sulfur
bacteria.
If all bacteria are
not destroyed by chlorination, the problem may return within a few weeks.
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. 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.
How Hydrogen Sulfide
Gas is 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.
If the Problem is in
the Well, Plumbing System, or Water Softener
Disinfect the well
and plumbing system with a strong chlorine solution. You can hire a licensed
well contractor to do this or refer to the Well Disinfection webpage for
instructions.
Sulfur bacteria can
be difficult to remove once established in a well.
Pre-work (such as
scrubbing the well casing, using special treatment chemicals, and agitating the
water before disinfection) may be necessary — especially if there are also iron
bacteria.
Contact a licensed
well contractor to do this pre-work.
If the bacteria are
in the water softener or other treatment devices, contact the installer,
manufacturer, or Minnesota Department of Health for disinfection instructions.
If the Problem is in
Groundwater
Installing home
water treatment or drilling a new well in a different formation are both
options.
Below are types
of home water treatment effective at removing hydrogen sulfide gas. Learn more
at the Home Water Treatment webpage.
· Activated carbon filters are effective for
hydrogen sulfide levels less than 1 milligram per liter (mg/L). The gas is
trapped by the carbon until the 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.
· The following are options are effective for levels both below and
above 1 mg/L.
o Oxidizing media
filtration (such as a manganese greensand filter) are effective for
hydrogen sulfide levels up to about 6 mg/L. This type of treatment is 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.
o Aeration and
filtration.
o Continuous
chlorination and filtration.
o Ozonation and
filtration.
Well
Management Program
Approximately
70 percent of all Minnesotans rely on groundwater as their primary source of
drinking water, and one million Minnesotans rely on private wells. Wells and
borings used for drinking water, irrigation, industry, groundwater monitoring,
heat pumps, hydraulic elevators, and other purposes must be properly
constructed, maintained, and sealed (filled with an impervious material) when
removed from service, to protect both public health and our invaluable
groundwater resources.
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