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Get Informed | Sulfate-Reducing Bacteria

What are Sulfate-Reducing Bacteria?

Sulfate-reducing bacteria obtain energy by using a carbon source to reduce Sulfate to hydrogen sulfide gas. These bacteria typically become established after the dissolved oxygen, nitrate, iron, and manganese in the water have been reduced; the water is in a reduced condition. For many water systems, the presence of these bacteria suggests a long-term microbiological problem with the water and not a short-term or recent condition. The only exception might be a source of water that is directly connected to a deep groundwater source, an anaerobic (no oxygen) lake sediment, or a wetland, all of which are in reduced conditions. This reduced condition may be experienced in groundwater sources that are experiencing contamination from a sewage source, a petrochemical source, and, perhaps, brine water. For a public water system, the presence of sulfate-reducing bacteria could suggest a cross-connection with a wastewater source or a distribution system with "stagnant" water and dead-end connections.

How Do Sulfate-Reducing Bacteria Become a problem?

These bacteria chemically change natural sulfates in water to hydrogen sulfide. Sulfur-reducing bacteria live in oxygen-deficient (reducing) environments such as deep wells, stagnant plumbing systems, stagnant distribution systems, biofilms in water softeners, and biofilms in water heaters. These bacteria usually flourish on the hot-water-side of a water distribution system.

Sulfate-reducing bacteria can cause the water to have a rotten egg smell, a metallic sheen, slimy coatings that appear yellow, brown, red, and or black, and a brown foam. These bacteria can create a nuisance and in some cases the biofilms have been associated with microbiologically-induced corrosion. Iron-reducing bacteria are also associated with elevated levels of iron, manganese, arsenic, and, in more extreme cases, metals associated with corrosion by-products like aluminum, copper, lead, and zinc.

What are the Health Risks for Sulfate-Reducing Bacteria?

There are no specific standards for sulfate-reducing bacteria, but there are standards for other groups of bacteria. There is a standard for total coliform bacteria (absent or none) and a standard for a "standard plate"count (< 500 colonies of heterotrophic bacteria per ml). It can be inferred that sulfate-reducing bacteria are indirectly regulated by the heterotrophic bacteria plate count standard because sulfate-reducing bacteria are heterotrophic and because a regulated water can not pose a nuisance or have a specific aesthetic problem. The presence of hydrogen sulfide gas may suggest the water is also impacted by a wastewater source that could contain a waterborne pathogen, such as: Pseudomonas, Citrobacter, Aeromonas, Salmonella, Escherichia coli and some species of Klebsiella, all of which also produce hydrogen sulfide (Source).

What are the Standards for Sulfate-Reducing Bacteria?

Although many impurities are regulated by drinking water standards set by the EPA, sulfate-reducing bacteria and hydrogen sulfide gas are not directly regulated, but the nuisances created directly by these contaminants (such as the smell and corrosivity of hydrogen sulfide gas) are regulated by most states through state-level primary and secondary drinking water standards.

When water contains as little as 0.5 ppm hydrogen sulfide it can be detectable by most humans. Concentrations less than 1 ppm give the water a "musty" or "swampy" odor and at 1-2 ppm hydrogen sulfide gives water a "rotten egg" odor and can make the water very corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 ppm, but have been reported as high as 50 to 75 ppm. Be aware that humans quickly lose the ability to smell hydrogen sulfide gas with continuous exposure; it is still there but you can no longer smell it.

Get Tested | Sulfate-Reducing Bacteria

There are warning signs of a potential problem with sulfate -reducing bacteria. First, you likely have a sulfate-reducing bacteria problem if your hot water has a sulfur-like odor. You may or may not have had a problem with a high standard plate count or total coliform bacteria but if the standard plate count goes up, or you noticed that when you returned from a trip away from home the water had a strange or musty smell, or the first flush of water from the tap was very gassy, discolored, had an off-taste, and had an odor, then you may have a problem with sulfate-reducing bacteria.

Level 1 | Observational Self-Testing

Level 1 Testing is done with simple observations that an individual can make with their own senses such as sight, smell, and taste. These observations can be readily apparent or can be observed as they change over time. In addition, accessible related information about the home can also be used to narrow down the cause of your water issues.

Notes on Level 1 Testing for Sulfate-Reducing Bacteria

The first place to help screen your water for sulfate-reducing bacteria is to look in places where your water sets, such as the inside of the toilet tank or water heating tank. If the inside of the toilet tank is discolored, typically black, and there are slimy coatings, and stagnant water in the piping has an initial rotten egg or musty odor with and without "blackish" water, you may have a problem with sulfate-reducing bacteria.

Observations for Sulfate-Reducing Bacteria

For sulfate-reducing bacteria, the aesthetic problems with the water are associated with the reduction of sulfate and sulfur compounds and other minerals associated with these compounds.   In some cases, the warning signs for sulfate bacteria may be a warning sign for a waterborne pathogen.

  • The water has a sulfur or sulfur-like odor.
  • The water is discolored and this discoloration is typically black and in some cases the black color will change to a reddish color if it gets oxidized.
  • The water has a high concentration of sulfate and the water is coming from a deep well or the source of water is anoxic, i.e., low in oxygen.
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Level 2 | Do-It-Yourself Testing

Level 2 Testing is Do-It-Yourself testing that can be done in your own home using a Testing Kit. After you’ve done Level 1 Testing, Level 2 Testing can confirm if your observations are correct. If your test results reveal the presence of a contaminant that is cause for concern, you can either proceed to determine the best treatment (see below) or continue to Level 3 Testing.

Notes on Level 2 Testing for Sulfate-Reducing Bacteria

Low-cost screening tests for sulfate reducing bacteria are is available but there are also inexpensive tests for the presence of hydrogen sulfide in drinking water. The primary warning signs would be black discolored hot water, intermittent hydrogen sulfide odors, and the presence of biofilms that tend to be black in stagnant areas of a distribution system.  In general, we would recommend conducting the Test Assured In-home Complete Test and checking for the level of hydrogen sulfide using some testing strips.

Through Amazon, you can purchase some "BART" testing kits to self-test for iron-reducing bacteria, sulfate-reducing bacteria, and slime bacteria, but please be aware that this may require you to take extra precautions when handling the material and disposing of the containers. If your private source has a bacterial problem, you may want to shock-disinfect the source and system using a Well Safe product.

Level 3 | Informational Testing

Level 3 Testing is done through an accredited Water Testing Laboratory. With Level 3 Testing, you can order a testing kit that is used to prepare your sample and submit it to the lab. By utilizing a lab, you have the assurance that a certified water expert had analyzed your water sample. If your test results reveal the presence of a contaminant that is cause for concern, you can either proceed to determine the best treatment options (see below) or continue to Level 4 Testing - Certified Testing.

Notes on Level 3 Testing for Sulfate-Reducing Bacteria

There are informational water testing kits that include nuisance bacteria, such as iron-reducing bacteria. Because sulfate-reducing bacteria can be associated with a waterborne pathogen, a corrosion problem, saline/brine water, or petrochemical contamination, it is typically wise to do more than just a simple test for sulfate-reducing bacteria. It is also not advisable to just test one sample, but it may be wise to test a "first-flush" or "flushed" sample and it may be necessary to test the water from the hot water system.

If this is a private water source, we also recommend ordering a National Testing Labs Basic Water Test Kit.  If this is a city water source, we recommend ordering the National Testing Labs City Water Basic Kit.

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Level 4 | Certified Testing

A Level 4 Certified Test Test uses chain-of-custody with a water professional coming to your home to prepare the water sample and then works with an accredited laboratory in order to certify your test results. This type of testing not only gives you the highest level of assurance in the accuracy of your test results, but can also be used as a document in legal cases. For Baseline Testing, we recommend that you use Certified Testing.

Notes on Level 4 Testing for Sulfate-Reducing Bacteria

Certified water testing is available for sulfate-reducing bacteria, but this evaluation should include a wider range of microbiological agents and other water quality parameters. Because the issue may be related to a stagnant flow system, the testing may need to include a "first-flush" sample and a "flushed" sample. If you need assistance with finding a certified laboratory, please Contact our team.

Get Treatment | Sulfate-Reducing Bacteria

To determine the best way to treat or manage an issue or problem related to sulfate-reducing bacteria, it is critical to understand the source of the contamination and the associated water quality. We recently had a regulated water system that had a reported problem with arsenic. During the on-site inspection we noted the water had a strong sulfur-like odor, we were informed a biofilm layer was clogging the intake, and the operator complained of a need to constantly increase the chlorine feed to maintain chlorine residuals. We tested for slime and sulfate-reducing bacteria; the well was positive for both. We decided to attempt to treat the well for the biofilm growth using a chemical additive. After purging the well, the yield went up, the arsenic level went down, and the nuisance issues were eliminated: NOT long-term treatment, just proper maintenance.

Short-Term Treatment

For well water users, our primary recommendation is to inspect your wellhead and shock-disinfect the well and distribution system. The shock disinfection should be done twice and the water lines should be flushed with all water treatment systems by-passed and in-line filters, and aeration devices removed. If you have a standard water heater, we recommend that the unit and the distribution lines in your home should be disinfected. If this is a city water source, it may be necessary to flush the water main and in some cases shock-disinfect the water heating system. This is why we recommend that homeowners on a city water system install a clear water filter housing immediately after the "city water" enters your home. If you are in an apartment complex, the issue could be related to a cross-connection or backflow prevention issue and stagnant water conditions within the complex. This condition can only be fixed by management. The installation of a carbon filter will not fix this problem for the long term.

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Long-Term Treatment

For city water customers, the long-term treatment is typically the responsibility of the water provider. Treatment may need to include increasing disinfection residuals in the water, changing piping, and flushing water lines. For city water customers with intermittent water quality problems, we suggest the installation of a barrier water treatment system that would include a whole-house backwashable particle filter (we do not recommend a carbon filter), a UV disinfection system, and then some point-of-use submicron particle filters. In some cases, individuals try to address this issue by treating the symptom, i.e., the hydrogen sulfide gas, using carbon filtration - This is not a good solution and we do not recommend it.

For private systems, the treatment process will depend on the water source and the extent or presence of other contaminants. For these systems, the first step is typically a combination of chemical oxidation/disinfection, a reaction tank, backwashable particle filtration (in some cases a carbon filtration system is advisable), and then any additional water treatment systems to address other water quality issues. In many cases, it is necessary to use a professional to install, manage, and maintain these systems. After the system is installed, it would be advisable to benchmark the system to ensure it is operating properly and then the system should be inspected and maintained regularly.

If you are using a water well or spring box, you may need to hire a contractor to chemically treat the well to address the combination of bioslimes, biological organisms, and associated chemical scale; the solution to the problem may be regular cleaning and maintenance and not installing a treatment system. The well may need some rehabilitation.

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