Bacteria, specifically the coliform group, is used as an indicator for the potential presence or absence of pathogenic or disease producing bacteria and other organisms. Some types of coliform bacteria called total coliforms are naturally found in soil and in surface water. Total coliforms indicate that surface water may be entering your well, which could cause contamination. Another type of coliform bacteria called E. coli or fecal coliforms are found exclusively in the intestinal tract of warm-blooded animals. An abundance of fecal coliforms present in a water sample will indicate contamination of excreta from warm-blooded animals, including humans, such as a failing septic system or runoff from a livestock area located close to the well. If virtually no coliform bacteria are found, it can be assumed that there are no pathogenic bacteria or organisms from fecal sources and that no surface water is entering a well. However, finding coliform bacteria in drinking water does not necessarily define the presence of pathogens, but only their potential for being present.

Water Sample is Unsatisfactory
A properly constructed water well usually obtains water from a depth at which bacteria is no longer present. Bacteria are usually filtered out as water slowly moves through the ground to the aquifer. However bacteria are found in upper soil layers, in surface waters, and can be concentrated in failing septic systems, livestock areas, and storm water runoff. There are several ways in which bacteria can contaminate your well:
  • Improper collection procedures. Please double check that the sample was collected carefully and according to the procedures supplied by the laboratory. You must be careful not to touch the inside of the bottle or cap because this will cause contamination of the sample. Sampling points should be selected carefully. Water that has been treated or softened should be avoided if possible and any screens or aerators attached should be removed to collect the sample.
  • Old shallow or dug wells are vulnerable to surface water contamination due to older methods of well construction. A new well maybe recommended to supply a sanitary source of drinking water.
  • Cracked, rusted, or improperly sealed well casings can allow bacteria contained in surface waters or wastewater to enter the well.
  • Faulty well seals that allow insects to enter and live inside the well casing can cause bacterial contamination of wells.
  • Cross connection or back siphoning conditions in the plumbing can cause bacteria contaminated water to be drawn into the water lines and could be siphoned back down the well. Back flow prevention devices are easily fitted, inexpensive, and are essential to prevent any risk of bacteria being siphoned into the well.
  • Improperly abandoned wells can be conduits for contaminated waters to reach aquifers. All landowners should be aware of potential risks and regulations of old unused wells. Indiana state law (312 IAC 13-10-1) requires "A well which has not been used for more than three months without being permanently abandoned must be sealed at or above the ground surface by a welded, threaded, or mechanically attached watertight cap. The well shall be maintained so that the well does not become a source or channel of ground water contamination."
  • Well location. If your well is located too close to a potential source of contamination, it can contaminate your drinking water. Your well should be located at least 50 feet from your or your neighbors septic system. Other potential sources of contamination include livestock areas, storm water runoff, and wastewater lagoons.
  • Flooding or ponding of water around your well can allow contaminated surface waters to enter the top of your well if the well casing does not extend high enough above the surface of the ground. Wells in pits below ground level are especially vulnerable to contamination from ponding water.
  • Repair or service of the well or water lines can introduce bacteria into the system. Water wells should be disinfected after any service or installation work.
If this is the 1st unsatisfactory bacterial result received, it is suggested that another sample be submitted. The most frequent cause of questionable results is contamination during sample collection. Pay particular attention to the instructions for sampling. If this resample comes back as satisfactory, there is no indication that the water is bacteriologically contaminated.

Disinfecting the Well
If the 2nd sample comes back as unsatisfactory, disinfection of the well should be considered. If, after disinfection, another sample comes back as unsatisfactory, the well should be inspected for a point of entry of contamination. If the well construction is such that surface water can drain or leak into the well along the outside of the well casing at or near the surface of the ground, this is sufficient to provide enough coliform bacteria to produce an unsatisfactory results. Consult a well driller or a plumber experienced in well problems to evaluate and possibly restore the integrity of the well.

Disinfection of the well is also recommended after any rehabilitation or construction work has been performed. Shallow dug wells frequently receive unsatisfactory sample analysis. Some of these wells are basically collecting near-surface water which is unlikely to be bacteria-free at all times. If a deeper, cased well is not feasible, it is suggested that bottled water be used for drinking and cooking or that water be hauled from a safe supply.

If you have any additional questions or concerns, contact your local Health Department at 765-423-9221.