Iron Bacteria and Sulfur Bacteria

Actually the correct terminology is “Iron Reducing Bacteria” (hereafter called “IRB”) and “Sulfate Reducing Bacteria” (hereafter called “SRB”).  IRB and SRB are troublesome to many people with well water.

Iron Bacteria presents many problems, so an accurate determination of its presence is crucial to appropriate treatment.  Iron Reducing Bacteria (IRB) cause aesthetic problems with the water such as taste, odor and staining of laundry and fixtures.  The most common indication of iron bacteria in the water supply is a reddish-brown or yellowish gelatinous slime in water tanks, faucets, toilet tanks, and plumbing. These nuisance bacteria may cause corrosion to treatment equipment, clog screens and pipes, and have a foul odor. Here are a few of the common problems associated with Iron Reducing Bacteria:

TASTES AND ODORS – Iron bacteria often produce unpleasant tastes and odors commonly reported as: “swampy,” “oily or petroleum,” “cucumber,” “sewage,” “rotten vegetation,” or “musty.” The taste or odor may be more noticeable after the water has not been used for some time. Iron bacteria do not produce hydrogen sulfide, the “rotten egg” smell, but do create an environment where sulfur bacteria can grow and produce hydrogen sulfide.

COLOR – Iron bacteria will usually cause yellow, orange, red, or brown stains and colored water. It is also sometimes possible to see a rainbow colored, oil-like sheen on the water.

RED SLIMY DEPOSITS – Iron bacteria produce a sticky slime which is typically rusty in color, but may be yellow, brown, or grey. A “feathery,” or filamentous growth may also be seen, particularly in standing water such as a toilet tank.

The characteristics listed above are typical of iron bacteria. However, objectionable stains, tastes, or odors may be due to other causes including iron, sulfate, hydrogen sulfide, manganese, or other nuisance organisms such as sulfur bacteria.  


Sulfur-reducing bacteria (SRB) live in oxygen-deficient environments. They break down sulfur compounds, producing hydrogen sulfide gas in the process. Hydrogen sulfide gas is foul-smelling and highly corrosive.  Of the two types, sulfur-reducing bacteria are the more common. The most obvious sign of a sulfur bacteria problem is the distinctive “rotten egg” odor of hydrogen sulfide gas. As with odors caused by iron bacteria, the sulfur smell may only be noticeable when the water hasn’t been run for several hours.  In some cases, the odor will only be present when hot water is run; this could indicate that SRBs are building up in the water heater. Blackening of water or dark slime coating the inside of toilet tank may also  indicate a sulfur bacteria problem.

Hydrogen sulfide gas produces an offensive “rotten egg” or “sulfur water” odor and taste in the water. In some cases, the odor may be noticeable only when the water is initially turned on or when hot water is used. Heat forces the gas into the air which may cause the odor to be especially offensive in a shower.

One of the many troubles with hydrogen sulfide is its strong corrosiveness to metals such as iron, steel, copper and brass. It can tarnish silverware and discolor copper and brass utensils. Hydrogen sulfide also can cause yellow or black stains on kitchen and bathroom fixtures. Coffee, tea and other beverages made with water containing hydrogen sulfide may be discolored and the appearance and taste of cooked foods can be affected.

High concentrations of dissolved hydrogen sulfide also can foul the resin bed of an ion exchange water softener. When a hydrogen sulfide odor occurs in treated water (softened or filtered) and no hydrogen sulfide is detected in the non-treated water, it usually indicates the presence of some form of sulfate-reducing bacteria in the system. Water softeners provide a convenient environment for these bacteria to grow. A “salt-loving” bacteria that uses sulfates as an energy source may produce a black slime inside water softeners.

Sulfur-reducing bacteria, which use sulfur as an energy source, are the primary producers of large quantities of hydrogen sulfide. These bacteria chemically change natural sulfates in water to hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient environments such as deep wells, plumbing systems, water softeners and water heaters. These bacteria usually flourish on the hot water side of a water distribution system.

Hydrogen sulfide gas also occurs naturally in some groundwater. It is formed from decomposing underground deposits of organic matter such as decaying plant material. It is found in deep or shallow wells and also can enter surface water through springs, although it quickly escapes to the atmosphere. Hydrogen sulfide often is present in wells drilled in shale or sandstone, or near coal or peat deposits or oil fields.  Occasionally, a hot water heater is a source of hydrogen sulfide odor. The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally occurring sulfates to hydrogen sulfide. 

Treating water containing IRB and/or SRB can be easily accomplished, but you must first determine if you have SRB and IRB and in what concentrations.

The best method to do this with the BART bacteria test.  You can find it HERE.

Bart Tests For Iron and Sulfur Reducing Bacteria



This article has 28 Comments

  1. I use a 1500gallon per day RO system, with sand filter, carbon filter, sediment filter and then RO membrane with a UV sterilising light in the permeate line for processing water that starts as 250TDS, but has a very bad taste and is also salty.
    My RO system produces permeate water with TDS of 55 as shown on my portable tester and the cncentrtate water still shows as basically 248-250 TDS.
    There is however a tendency for the flow meter for the permeate on the RO unit to turn light brown over time and kettles used for boiling the water have a light brown deposit develop on the sides and bottom over time.
    Is this anything to do with Iron?
    Does the RO unit not remove Iron.?
    It’s not a huge problem and I di drink the water with seemingly no ill effects, but I have this light brown deposit thing nagging in the back of my mind?
    Will a 50micron filter take care of such a thing if I put it in the permeate line?

  2. We definitely have sulfur. The rotten egg smell is OVERPOWERING and taking a shower is not enjoyable anymore. We rent directly on a lake… within 20 ft of our door. Could that contribute? Our landlord days it’s just iron that everyone deals with on the Lake, but it’s definitely sulfur as well. My brand new washing machine is getting scaly & slimy. What do I do???

  3. How can we resolve the odor that comes from the water? It is a rotten egg odor and is worse in the hot water. After running the cold water for a bit it sometimes goes away. The inside of the toliet tank has brownish stuff growing in the sides. I just cannot live like this. What do we have to do to fix it? It stains our white clothes a brownish color and I cannot stand the smell. Sometimes it has a yellowish tint to it

  4. Recently my water softener was causing low water pressure in the house. I used ResCare cleaner twice and pressure has appeared to return to normal. But I just discovered orange slime in toilet water tank after noticing black in the bowl as if always dirty. I am on city water not well. Is the softener the source of the problem?

  5. I’m suffering here with super salty and brown hot water, we use a braswell 2 tank system on a shallow well.. we have had 4 tech’s out, and no-one can seem to help us. Since my animals can’t drink it, we may have to move!- would this system help us?

  6. This is driving me nuts. I have the sulphur smell in only one faucet, only on the cold side, and only when initially turned on. I’ve backwashed that line with a chlorine mix (PEX, so I can disconnect that line easily in the basement), which kills the smell for a couple of months, and it comes back. What drives me crazy is I don’t smell it on any other faucet, shower, washing machine, etc., either cold or hot. No slime in toilets, black residue, etc. Any ideas?

  7. Hi Mark,

    We live in north central Illinois and are on a well. Sulfur smell is a problem in our area. We currently use a system that incorporates a 20″ 5 micron pre-filter followed by peroxide injection and a back washing carbon tank to combat the sulfur. Monthly, the pre-filters are changed due to being fouled by an orange, sometimes black substance. The carbon tank gets re-bed about every 2-3 years. Water quality changes with the weather, best when it’s summer and worse in the winter. The water clarity varies too. Sometimes it’s bright and clear, other times it has a greenish tint accompanied by a swampy odor. Been dealing with this for about 9 years. Any suggestions?

  8. Use Two Pre-Filters as step-down Filtration: with 20 and 5 micron filters

    Use this with the Dual Injection Panel:

    Add a second Catalytic Carbon Tank and inject peroxide ahead of each tank in Series, not parallel. It’s expensive, but effective.

  9. Our water has 140,000 MPN/mL of IRB. We do notice a red/brown slime in the pipes. But also we are having a burning sensation on our tongues and skin breaking out when we drink the water and have stopped using our well water all together. Can this be caused by the high IRB concentration or is it something else?

  10. HI Mark,
    I recently bought a1958 home just outside Atlanta, GA. I believe I’ve discovered Iron Bacteria in our water, but am struggling to find out where it is coming from. The evidence I’ve seen is this- We have a heavy duty 14 stage water filtration system, and one of the filters is continually getting completely clogged with a red/brown substance. When I take the filter out and collect a water sample, a fluffy brown slim settles at the bottom resembling the iron bacteria examples I’ve seen from research. Additionally, water occasionally comes out of the faucets a tint of brown/red color. We have copper pipes under the house, cast iron drain pipe, and from what I can see at the water meter, a white plastic main water line. I keep reading about iron bacteria primarily being an issue in well water, but we are on city water. I am struggling to decide where to start to fix this! Our home is approximately 200 feet from the meter. Could we have a leak somewhere in the pipe causing the issue? Any guidance would be much appreciated.

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