What are coliform bacteria?
Coliform bacteria originate as organisms in soil or vegetation and in the intestinal tract of warm-blooded animals (fecal coli). This group of bacteria has long been an indicator of the contamination of water and possible presence of intestinal parasites and pathogens. The coliform bacteria are relatively simple to identify, are present in much larger numbers than the more dangerous pathogens, and react to the natural environment and treatment processes in a manner and degree similar to pathogens. Thus by observing coliform bacteria, the increase or decrease of many pathogenic bacteria can be estimated.
Where are they found?
The many sources of bacterial pollution include runoff from woodlands, pastures and feedlots; septic tanks and sewage plants; and animals and wild fowl. Domestic animals contribute heavily to the bacterial population. Many coliform bacteria enter natural streams by direct deposition of waste in the water and the runoff from areas with high concentrations of animals or humans.
How could they enter a water system?
The most likely sources come from where the water is used, the spigot, sink, or unclean containers. Another source includes backflow from a contaminated source, a sink-top carbon filter, bucket of water, or puddle at the end of a hose. Also, reduced pressure or suction in long water lines, or drawing in soil water at the joints are sources as well.
Why test for coliform bacteria?
While most coliforms are not pathogens, they serve as indicators of the microbial quality of water. Public health officials have tested for total coliform bacteria and fecal coliform bacteria for most of this century as a way of checking the quality of water.
Pathogens – the bacteria, protozoa, and viruses that make people sick – can be rare and difficult to detect even if they are present in the water. Total coliforms are indicators and are more common and easy to grow. Testing for them provides a margin of safety. Pathogens may not be present if coliforms are, but it would be wise to look for problems just in case.
Total coliforms are mostly natural residents of soil and water. Fecal coliforms are those that are usually found in the fecal material of animals. Their presence usually means that the water may be contaminated by sewage effluent. Finding the source of the problem and correcting it is very important.
Should I have my water tested?
The question of whether or not to have your water tested is a serious one that concerns the health of you and your family. Your water should be safe to drink and acceptable for all other household uses.
If you obtain drinking water from your own well, you alone are responsible for assuring that is safe. For this reason, routine testing for bacteria, nitrates, and anything else of concern, even if you do not perceive a change in your water, is highly recommended.
Even if you currently have a safe, pure water supply, annual testing can be valuable because it establishes a record of water quality. This record can be helpful in solving any future problems and in obtaining compensation if someone damages your water supply. You should also have your complete water supply system annually inspected by a certified and/or licensed water supply professional, such as a ground water contractor.
When should I test my water and what for?
The total coliform (TC) test that is usually mandated as a standard of “safe” water supply is a place to start. It is used to detect indicators of possible surface contact and therefore potential contamination. If the test has not been run regularly, the time to start is now.
The TC test will not detect the large majority of biofouling organisms or even most bacteria in a well. Note 1: It is not uncommon for wells showing no coliforms to have very large bacterial populations.
Note 2: Some “native” bacteria will cause a “positive” coliform reaction in the total coliform test, but take any positive as a reason to look for possible problems. Once each year, test for coliform bacteria, nitrate, and anything else of concern. It is best to do this during the spring or summer following a rainy period. These tests should also be conducted after repairing or replacing an old well, pump, or pipes, and after installing a new well or pump.
You may also wish to test during the following circumstances:
- If family members or houseguests have recurrent incidents of gastrointestinal illness
- If an infant is living in the home
- If you are buying a home and wish to assess the safety and quality of the existing water supply
- If you wish to monitor the efficiency and performance of home water treatment equipment
- If you notice a change in the taste, smell, or appearance of the water
How should a water sample be collected?
Most testing laboratories or services supply their own sample containers. Use the containers provided and carefully follow the instructions given for collecting, preserving, and handling water samples. Samples for coliform bacteria testing must be collected using sterile containers and under sterile conditions.
Some procedures require that water runs from an inside tap for several minutes before filling the sample containers. Other instructions ask you to collect samples in the morning after water has been confined in the pipes overnight. Laboratories may sometimes send a trained technician to collect the sample or to analyze the sample directly in your home.
If I have bacteria in my well, where do they come from?
Many experts in public health and water supply used to think that the subsurface was some kind of giant filter that trapped microorganisms before they could get to ground water, resulting in an effectively sterile water resource. However, we now know that many types of bacteria are native or adapted to saturated sediments and rock, and are indeed present in significant numbers in most water supply aquifers, even deep formations.
Given time and a route (soil and rock provide plenty of both), bacteria will migrate into and take up housekeeping in an aquifer. The environment is really rather nice- quiet, lots of surface area, often adequate carbon sources, and moderate temperatures with little environmental change.
Drillers and pump installers/servicers can also introduce microorganisms during their activities, but should not be considered the primary source of native microorganisms. There is no practical way at present to say for certain what is the source in any one well- maybe someday, but not yet. “Non-native” coliform bacteria or “protozoa” of potential health concern such as Giardia and Cryptosporidium are most likely introduced from the surface.
Where else could coliform bacteria come from?
Don’t always blame the water first. Who sampled the water and how? How sanitary are your practices in food handling, personal hygiene, etc.? Do children wash regularly? While uncomfortable and personal subjects to some, these are more likely routes for contamination than the water itself.
Will coliform bacteria make us sick?
Maybe, maybe not. Coliforms are not one kind of bacteria, but many. They are defined by what they do- grow on the sugar, lactose (the same as found in milk), and employ enzymes to help them use this sugar.
Most coliforms are harmless residents of soil and will not make people sick. Some strains of E. coli, the most common fecal coliform bacterium (usually living in animal fecal material), may be pathogens. Some found in food have been lethal. Their presence should be taken very seriously.
Your immune system also determines whether or not you will become ill. People become accustomed to the natural bacteria in their water while guests used to other water may have some discomfort or diarrhea. Immunocompromised individuals may become ill under circumstances where people with normal immune systems would not and such individuals should be very careful of the water they drink.
Pathogenic (disease-producing) organisms occurring in water range from ultra-small viruses to microscopic bacteria to relatively large protozoa (cysts). Basically, three types of pathogenic organisms can affect the safety of water: bacteria, viruses, and protozoa.
Bacteriologic and protozoic pathogens are known to cause typhoid, dysentery, cholera, and some types of gastroenteritis. Conventional wisdom is that contamination of ground water with protozoa indicates surface water influence. Viruses account for more than 100 human maladies including polio, infectious hepatitis, and some forms of gastroenteritis. In general, viruses are more poisonous and more resistant to disinfection than bacteria.
If my well has bacteria, should we drink bottled water?
If you have unsafe levels of coliform bacteria you should obtain an alternative source of drinking and cooking water until the problem is solved. Don’t neglect to solve the problem. Most bottled waters are not free of bacteria, but they should be free of coliforms. In the U.S., the Food and Drug Administration administers commercial bottled water quality.
The source (bottler) should be able to give you information on the quality of the batch of bottled water you are using. Another source is water hauled from a nearby public water system that is tested to be safe for drinking. It is important that water jugs or tanks used to haul water are themselves very clean and free of coliform bacteria or chemicals.
What types of treatment devices will make the water safe for consumption?
If treatment is necessary, there are a number of ways of addressing bacteriological concerns. Disinfection is the removal of infectious agents. Disinfection should not be confused with sterilization, which is the complete inactivation of living material. Water and wastewater disinfectants are potent biocides.
The disinfectant concentration and contact time are the prime factors in the inactivation of a microorganism. The product of the concentration and contact time for a specified level of kill (99%) provides a useful term to compare disinfectants and factors affecting microbial inactivation. The contact times for each disinfectant are variable.
Biological contaminants are most effectively eliminated through chlorine disinfection, filtration, ultraviolet irradiation, and ozonation. All methods must be properly designed for the intended use and properly maintained. Additionally, bacterial analysis of the treated water must be made with sufficient frequency to ensure adequate treatment.
A disinfectant should be effective on many types of pathogens regardless of their quantity and it should be able to kill all pathogens within a reasonable retention time. The chemical should also be safe and easy to handle and it should not make the water toxic or unpalatable. In addition, the concentration of disinfectant in the water should be easy to monitor and the disinfection should provide residual protection against possible recontamination. Lastly, the disinfectant should be readily available at a reasonable cost.
Disinfectant dispersing equipment should also fill several requirements. The equipment should be automatic, require minimal maintenance, and treat all water entering the home. It should also be fail-safe so that no one can unknowingly use or consume untreated water.
Treatment methods include:
- Ultraviolet irradiation
- Silver treatment
All of these methods require proper maintenance, just as the well and the rest of the water system require regular and proper maintenance and service by a qualified professional.
What steps can be taken to determine if there is a contamination problem somewhere on our property?
A sanitary survey is the best way to determine private water system vulnerability. Vulnerable wells could include those with inadequate setback distances from potential sources of contamination (such as septics), inadequate well construction, and high flow hydrogeologies.
Consider well site factors:
- Site wells in locations not vulnerable to pathogens
- Consider horizontal and vertical setback distances from sources of fecal contamination to a well
Consider hydrogeological factors:
- Depth of unsaturated zone
- Confining layers
- Fractured and porous soils
- Land use patterns
Ensure protection of the distribution system:
- Well construction to codes
- Cross-connection control
- Backflow prevention
- Age of the well and its components
Ensure proper maintenance of the well and its components. Be sure to schedule an annual water well checkup.
Changes in taste, odor, or turbidity may signal something has changed. Have your water tested by a qualified laboratory annually, when work is done to your system, or when there is any change in taste, odor, or appearance. Water labs are listed in your phone book under “Water Testing” or “Laboratories.”
How do we prevent this from happening again?
If possible, do whatever it takes to correct the problem in your existing system. If necessary, install a new well and water inlet system, bringing it up to your state’s code and good industry practice. Hire experienced water well drillers who are certified and/or licensed in your state and come recommended to you. Look for quality – not price – first.
If my neighbors have coliforms in their water, will we get them in ours?
It depends on the source in your neighbor’s water supply. It is common for contaminated and uncontaminated wells to be very close by. The reason is that most bacterial problems happen right at the well or after the water leaves the well.
If some people in our area have wells contaminated by bacteria, should we try to hook into public water?
Generally, area-wide coliform contamination is very rare. Usually the problem is at the wells or drinking water source, or may be due to faulty waste disposal on vulnerable land (shallow bedrock, for example).
Look to your own source. If the costs of upgrading, property values, etc. exceed the cost of hooking to public water (seldom the case) then hook up. Also, if your ground water source is poor in quantity or quality, and solutions are too expensive or too much trouble, then hook up. Do not accept reasoning from neighbors or water districts that if some wells are contaminated, they all are, or that the only solution to low yields or poor quality is municipal water.
What about bacteria in public water systems?
About 40,000 of the 210,000 ground water-supplied public water systems reporting via the Federal Reporting Data System have had microbial violations, indicating bacterial presence in their ground water, wells, or distribution systems during the last five years. Smaller systems and non-community systems tend toward violations from source water contamination.
Contamination of distribution systems results from cross contamination and backflow events, and from bacterial growth within a system. Some septic systems, displaced by rising ground water pressure or flooding, may become hydraulically connected to wells. They are the most frequently reported causes of contamination in ground water disease outbreaks associated with the consumption of untreated ground water in the U.S. Other sources are animal feedlots and the like.
If my water is clear and smells OK, is it safe?
You cannot directly smell unsafe bacteria or protozoa. They can only be detected using tests designed for that purpose. You should check your water quality regularly. Some sources of odors are bacteria or septic, or the presence of chemicals. It is a good idea to take your nose seriously. Have the water tested.
What if my water is brown, or black, or smells bad?
The water may not be unsafe to drink, but you should test it just in case. Also test for “iron bacteria” or biofouling, iron, manganese, and sulfur. Water treatment methods are available to provide clear, odor-free water. Check with several water treatment professionals for options.
How common are water problems?
“Pure” water does not exist – all natural water contains some gases and minerals. All natural waters, regardless of their source (surface or ground water), are likely to contain some microbial organisms. A few cause disease; some impart taste, odor, or turbidity (cloudiness) to the water; others are beneficial.
The acceptability or desirability for the presence of these materials in water is usually a matter of individual preference. Many people develop a tolerance for drinking water of poor taste, odor, or appearance, and they believe their water supplies do not need treatment. They should still have their water supply tested every year or after well and/or pump service. If a water quality problem is present, it can usually be remedied with the appropriate water treatment equipment. Changes in taste, odor, or turbidity of the water may be the first signals of a water problem.
Most water bacteria are harmless and many are actually beneficial. They consume organic debris, thereby reducing the water’s chemical oxygen demand; prolong the useful life of filters; and destroy some foul tastes, odors, and colors. In addition, some produce by-products that kill or inhibit growth of some pathogens. Since pathogens are usually less numerous and less hardy in water than are other bacteria, their survival can be decreased by ordinary competition for food with more vigorous organisms.
Disease may be transmitted by the consumption of contaminated water and shellfish or close-contact recreation. The human pathogens of major concern in drinking water and shellfish consumption follow the anal-oral route of transmission. The pathogen must enter the host through an appropriate portal, overcome the host’s defenses, and proliferate to a sufficient degree to cause symptoms of disease. This contamination results from human and animal fecal matter migrating from surface deposition or from septic systems or leaking sewer lines.
Are people getting sick from drinking water?
The Centers for Disease Control and Prevention issues an annual survey of foodborne and waterborne disease outbreaks. For the two-year period 1999-2000, 25 states reported 9 outbreaks associated with water intended for drinking. The outbreaks caused an estimated 2,068 persons to become ill.
During the same period, 59 outbreaks from 23 states were attributed to recreational water exposure, affecting an estimated 2,093 people.
What requirements do public and private water systems have for dealing with bacteria?
All community public water systems, as well as non-community public water systems (public systems that do not serve a residential population), must submit samples for coliform bacteria testing on a regular monthly basis. Failure to submit samples, meet the maximum contaminant level (MCL), and report non-compliance are all violations of the rule.
However, remember that the sample is probably not taken inside your home. Parts of your own household plumbing may be a source of bacteria in your own drinking water. The maximum contaminant level is based on the presence or absence of total coliforms in a sample (the old maximum contaminant level was based on an estimate of coliform density). A very small water system may have one coliform positive sample per month and still remain in compliance with the regulation.
Each state may have its own unique requirements for disinfection and water quality monitoring of public or private water systems. Check with your state water agency to determine what is required in your state.
How do coliform bacteria survive?
Bacteria require a food source and warm, moist conditions for maximum survival. Although once in the water the coliform bacteria begin to die, they are most likely to survive in deep, slow moving, heavily polluted waters that lack dissolved oxygen.
The survival of coliform bacteria in soils depends on the soil’s characteristics. Survival is much less likely in well-aerated soils. However, several other factors must be considered. For example, a sandy soil may be well aerated and have a low bacterial survival rate. If the depth to ground water is small and the water flow rate through the soil is fast, the bacterial contamination of the ground water may be high.
In contrast, a heavy soil, with slow water percolation rate and long distance to ground water, will have a higher bacterial survival rate than the aerated sand. However, the long period of flow may allow enough time for the water to be filtered before it enters the ground water.
How do ground water contractors minimize the possibility of well contamination during drilling and pump service?
Despite the fact that the most likely source of a microbial population in a well is the aquifer around it, drillers and pump contractors are widely accused of transporting the bacteria about. Drilling and well service cannot be sterile, but some steps are available to minimize the possibility of such transport.
Any individual following the steps listed here should be credited with doing all that is feasible to avoid contamination.
- Becomes familiar with local problem wells.
- Minimizes practices that introduce or harbor bacteria during drilling, jetting development, and hydrofracturing.
Repeat: drilling and well completion are not sterile pursuits and never will be. Like anything else in the environment, the rig, tools, etc. are covered with bacteria, even when clean.
- Develops thoroughly after drilling and always chlorinates after development or after pump service. Well development removes drilling damage and mud that hide microorganisms, and also provides for a more effective well intake area to minimize the effects of biological buildup when it occurs.
- Always chlorinates after development or pump service to the state’s recommendations (usually 100 ppm or so minimizes contamination due to drilling and service activity).
- Keeps tools as clean as possible. After well development or redevelopment, drillers should clean tools thoroughly (to the clean steel). Keeps casing, riser pipe, pumps, etc. off the ground and out of the mud. Never reinstalls any pipe with any encrustation, mud, or film of any kind without thorough cleaning and chlorination.
- Always has proper water analyses run on a new well whenever it is serviced. These include total coliform bacteria and chemical parameters useful to both health and safety, and general water quality (nitrates, hardness, iron, etc.). Proper sampling is crucial. If sulfur or iron bacteria are a problem, tests can be run to analyze these as well.
Is the air gap for backwash or reverse osmosis concentrated sufficiently to prevent backflow?
Check for corroded water lines by having an experienced plumber check these possibilities. The well construction itself should be examined. If the well top is buried, in a pit, or submerged (or you can’t find it at all) chances are it leaks and introduces poor quality water. Older wells may not have been sealed properly or may be corroded.
Other possibilities include leaking well caps or seals, leaking pitless adapters, or water line leaks. Poor fitting or damaged well caps permit small animals, insects, etc. to crawl into the top of the well. As they die and fall into the water, they decompose and may contribute coliform bacteria.
The well pump should be well below the pumping water level if possible, and the water in the casing regularly flushed out. Make sure on-site wastewater treatment systems are correctly designed, maintained, and functioning properly. Have a person experienced with these systems check it out.
What’s the difference between chloroform and coliform?
These words sound very similar. Chloroform is a form of chlorinated organic chemical, a VOC (volatile organic compound), and coliform describes a group of bacteria that grow on certain types of growth media, or cause a color change when incubated that tells the analyst that these bacteria are present.
When you are concerned about a water problem, what do you do?
Have your water tested by a qualified laboratory. Your local health department is typically the first stop. They will either do a free or inexpensive test for the presence of bacteria, or refer you to a qualified laboratory. To test for other substances, such as metals or chemicals, a more extensive and expensive sampling and testing program would have to be conducted. Independent laboratories will probably be required.
Testing should be conducted by a certified drinking water laboratory. The U.S. EPA offers a state-by-state listing of certification officers, or call the National Ground Water Association at (800) 551-7379. The certification officer in your state can provide a list of certified labs in your area.
How do I find a qualified water treatment specialist?
You can find listings of water treatment specialists in your phone book under “Water Conditioning” or “Water Treatment.” Be sure you speak about water treatment and not water conditioning such as softening.
Where can I get more information?
This document, which may be amended from time to time, was prepared by National Ground Water Association staff utilizing information resources of the National Ground Water Information Center, state regulations, state water agencies, state extension services, and others. Special thanks to NGWA member Stuart Smith, Smith-Comeskey Ground Water Science, Ada, Ohio.