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What is Biofilm and How Does It Affect My Water?

Biofilm is simply a layer of bacteria and their secretions and waste products. It accumulates on every surface that is exposed to water containing the appropriate nutrients to support bacterial life. Unlike humans, bacteria can "eat" iron compounds, sulfur compounds such as sulfates, organic matter such as sloughed off skin or other dead microorganism, and a wide variety of other substances. They can also make incredibly "sticky" glue-like substances to attach themselves to surfaces and to one another. This combination of bacteria, their byproducts, and the sticky polysaccharides and proteins they make constitute a biofilm. Once established biofilms are almost impossible to remove or penetrate with disinfectant chemicals. Usually they must be removed physically or the plumbing or affected appliances must be replaced.

If there are no bacteria, there is no biofilm. If the bacteria lack food to grow they do not develop a biofilm. If other growth conditions are outside their ability to adapt, the bacteria will not grow. But typical well and tap water have bacteria, and nutrients, and conditions conducive to growth, so biofilms almost always develop and begin doing damage.

The initial residents of biofilms are able to convert inorganic molecules like sulfate, nitrate, carbon dioxide, and others into organic molecules. These organic molecules then feed new microorganisms that could never have grown there before. Some of these new microorganisms are disease causing in humans, and can therefore pose a threat to health. Legionnairres pneumonia is caused by one of these organisms.

Biofilms will develop on all filtration and purification equipment.  When they do, they render the filtration /purification devices ineffective because the bacterial film on the surface of the filter media keeps the water from coming in contact with the part of the filter that is designed to remove the contaminant. No one would know this is happening because it is a gradual (weeks to months) process and most of the contaminants that slip through have no odor, taste, color, or other quality that is detectable by human senses. You must test to know. The only time people notice a biofilm has formed or realize they have a problem is if there is also sulfate in the water and sulfur reducing bacteria convert it to hydrogen sulfide (rotten egg odor). These folks get stinky water, which lets them know they have a biofilm and often motivates them to take action.

Biofilm growth can be prevented or inhibited by proper water treatment and maintenance. If nutrients are removed (ex Sulfate or Iron) bacteria will not grow. If bacteria are growing, chlorine shocking will inhibit their growth or kill them outright, but only if the biofilm is not too far developed. In a thick biofilm, the disinfectant can never reach the organisms, so they are protected, and unaffected - even when very high levels of chlorine, bromine, or other disinfectants are use. In this case a permanent chlorine "feed" system may need to be installed to kill bacteria as they grow. If the film is thin then sometimes it is possible to kill all the bacteria with a single shock chlorination. The only way to know is to test the water about 3 weeks after shock chlorination for the presence of certain bacteria. See bacterial testing.

So ideally, you want to stop this process from the very beginning. A new house with a new well, if properly tested, treated, and maintained will reduce or eliminate the health risks caused by biofilms.

What does biofilm look like?

Notice the biofilm that has grown on the inside of the bottle above. This is what happens to your purification /  filtration system and plumbing if it is left untreated. This was a sample collected from a client's well and left standing in a refrigerator for several weeks. It was clear and uncolored when it was collected.


         Before                      After-Iron                   After-Sulfur       

Leftmost is a culture tube just after addition of a water sample. Notice the water is clear and the residue at bottom is sterile "food" to allow for growth of bacteria if they are present. The middle tube shows iron reducing bacteria after only 3 days incubation. The rightmost tube shows the deposits left by sulfur reducing bacteria that were obtained in a sample from a household well after 13 days incubation. Note that both the positive tubes had clear liquid at the start. All discoloration and a visible deposit is just what happens in your well, plumbing, and purification system if these bacteria are present.

But who ever looks inside their water pipes, or at the bottom of the well, or inside their pumps, water heaters, or even their toilet tank?

Well now you don't need to. Just call us, tell us you want to know whether or not you need to treat your system to prevent further damage by biofilm producing bacteria, and we will test your water for you, and give you instructions on what you can do if there is a problem.


Home Sediment Filters / Water Filters

Standard home water/sediment filters are like sieves that hold back only large particles. Virtually ALL toxic chemicals and most bacteria, viruses, and parasites, and many other particles are small enough to pass through this "sieve" and can therefore enter your home's drinking water when they are present.


Do your filters look like this?

If so, toxic chemicals are not being removed and you may have "harmless" bacteria in your system. The same "harmless" bacteria that are present in your toilet tanks, sinks, on countertops, and in other places you probably disinfect on a regular basis with Lysol, bleach, and various antiseptic lotions and sprays.

Testing provides the information needed to decide whether or not bacteria are present, whether they can be controlled by nutrient limitation, which bacteria are present and thus what purification technology will work. Once completed, you can be sure of a drinking water quality that exceeds the best municipal, well, or bottled drinking water. The money saved by not needing to buy bottled water alone will return all testing cost in less than one year, and the additional money saved through energy conservation and longer appliance life is an added bonus. See our section on how to choose which tests to request on a first water test. 

 (How to Know What to Test For)




Remember We work for you. Not the government or a company selling filters or water. For help, Call AWSA at 1-866-626-1716 or go to


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Last modified by Dr. Eberhard Essich 03/22/17