What is well disinfection?

Properly constructed and maintained water well systems are designed to keep microorganisms such as bacteria, viruses, and protozoa from getting inside the well system and into the water. When a water test indicates the presence of microorganisms in a well, disinfection of the well system is recommended along with some level of inspection.

Where do these microorganisms come from and how harmful are they?

Wells are routinely tested for coliform bacteria, which come from soil or vegetation, and in the intestinal tract of warm-blooded animals (fecal coliform bacteria). The many sources of bacterial pollution include runoff from woodlands, pastures, and feedlots; septic tanks and sewage plants; and animals (wild or domestic).

Most coliforms are harmless residents of soil and will not make people sick. Some strains of E. coli, the most common fecal coliform bacterium, may be pathogens. Some E.coli found in food have been lethal, so their presence should be taken very seriously. Testing for coliform bacteria is inexpensive and their presence indicate that harmful, pathogenic bacteria could possibly enter or exist in the well. So, if a well tests positive for coliform bacteria, follow-up testing for E.coli sometimes is recommended depending on the specific lab test results. Some coliform tests can provide results for both total coliform bacteria (the indicator) and E. coli, the sign of fecal contamination and potential pathogens.

The federal standard for bacteria in public water systems is zero presence. While private, household wells are not regulated by the federal government, public health authorities recommend that private well owners also keep their well water free of all coliform bacteria. A sanitary well water is not entirely sterile (free of bacteria) but may contain naturally occurring, harmless to health, bacteria in low numbers. Appearance of slime (biofouling) buildup in water system components indicates a need for cleaning to prevent potential sanitary issues.

When should a well be disinfected?

A water well should be disinfected:

  • After construction of the well and before the water is consumed. Water from a newly constructed well should test free of bacteria before the water is used.
  • After an existing well is serviced. Any time a water well system is opened up, it creates the potential for bacteria to enter the well, so disinfection after servicing helps ensure the water is free of bacteria.
  • If there is a visible defect in the well system that could enable bacteria to enter the well. Examples of such defects are a cracked or loose well cap, or damage to the well casing (the vertical pipe that extends above the surface of the ground).

Who is qualified to disinfect a water well?

The National Ground Water Association recommends that qualified water well system professionals disinfect water well systems. Because proper well disinfection involves chemistry and proper application techniques involving specialized equipment, the potential is great for well owners to not properly disinfect their well systems—or even cause damage to their well systems or personal injury.

Common problems with well owners attempting to chlorinate their own wells include:

  1. Over-chlorination and damage to well equipment
  2. Poor distribution of chlorine compound, resulting in damage to casing, pipe, the pump and pump wire
  3. Inadequate contact time between the disinfectant and microorganisms in the well
  4. Failure to remove disinfection-inhibiting factors from the well, thus impeding disinfection effectiveness
  5. Inability to understand or follow proper disinfection instructions.

Also, chlorine compounds are powerful oxidants that induce chemical reactions. If spilled on grease or oil, the potential for explosion or ignition exists. Breathing chlorine dust or concentrated chlorine vapors can cause damage to mucous tissues.

What is used to disinfect a water well?

Chlorine compounds are most commonly used as a disinfection agent in water wells. However, NGWA does not recommend that household bleach be used to chlorinate a water well, in part, because:

  • It is not made for use in drinking water
  • It is not the most effective form of chlorine for well disinfection
  • It has a poor shelf life, which reduces its potency.

NGWA recommends that water well system professionals use disinfection products certified for drinking water use by NSF International (an independent product testing organization), or other appropriate authorities.

What does it mean if bacteria keeps returning after disinfection?

If a well is properly disinfected, but follow-up water tests show the bacteria have returned, this could indicate the need for action beyond disinfection. Sometimes recurring bacteria in a well can indicate:

  • A breach in the well system, for instance, a problem with the well casing, pitless adapter, or well cap.
  • A concentrated contamination source such as a failing septic system or an animal feedlot that adversely affects groundwater quality in proximity to the well.
  • The well needs to be cleaned because debris in the well is preventing disinfectant from making contact with microorganisms.

A qualified water well system professional is best suited to investigate the possible causes of recurring microorganisms in the well. While components of a well system above the ground surface can be inspected visually, other well components are in the subsurface and require the kind of special diagnostic techniques that water well system professionals use. If the presence of bacteria is recurring, consult with a qualified water well system contractor, who can advise you on how to proceed.

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