ON-SITE WATER SUPPLY DISINFECTION MANUAL
Natural ground water from all but very shallow aquifers is considered free from pathogenic (disease causing) bacteria and viruses (Bouwer, 1984).
As such, ground water obtained from properly designed and constructed water wells is generally free of disease causing bacteria, and continuous disinfection is unnecessary (Roscoe Moss Company, 1990).
However, disinfection of a new or repaired water supply system is needed to remove contaminants introduced during the construction or repair process (Driscoll, 1986).
Existing water supplies require disinfection when routine maintenance of the system takes place, or when the results of water samples show the presence of coliform bacteria (Driscoll, 1986).
This manual provides information to water well drilling contractors, local health department (LHD) sanitarians, and others involved in potable water system construction, operation, or evaluation.
Disinfection is the inactivation or destruction of pathogenic organisms through the disruption of the organisms’ normal life processes (Connell, 1996).
Disinfection does not mean sterilization.
The result of effective disinfection is the production of potable, or drinkable, water.
Throughout this manual the authors promote the concept that “disinfection,” when applied to water well system construction,
should be considered from a broader perspective than merely the application of chemicals to achieve microbial inactivation.
Disinfection is a process that includes the following
components:
1. Proper water supply system preparation, including the sanitary completion of the water well, the cleaning of existing wells, and the proper development of new wells.
2. Thorough flushing of the water supply.
3. Treatment with a properly prepared chlorine solution.
4. Collection and analysis of water samples.
Although there are several chemical disinfectants that may be used to treat a well, this manual only addresses the use of chlorine, the most commonly used water supply disinfectant
When a new water well is drilled or an existing water well or household piping is repaired, bacteria can be introduced into the water system (Campbell, et al., 1973).
Treatment with chlorine, combined with proper well preparation and flushing, usually eliminates the bacteria.
Water well drilling and pump installation contractors are responsible for
disinfecting the work they perform.
Once a properly constructed water well has been properly disinfected, it should produce safe water consistently without the need for continuous chlorination.
The bacteria used as an indicator of contamination are coliform organisms, normally found in the intestine and feces of warm-blooded animals.
Their presence in the water supply indicates a serious potential for illness-causing bacteria or viruses to be present.
If a water sample from a new, repaired, or existing well is positive for coliform bacteria, an immediate repeat sample is an essential step to confirm the risk.
Consuming water with coliform bacteria is not recommended and appropriate advisories should be issued to persons who use the water system.
A positive coliform water sample does not always mean that the water well itself is contaminated.
The well could be producing coliform-free water while a bacteria problem exists in the household plumbing.
Collecting water samples from different points can then help pinpoint the location of the problem.
Disinfection should be performed by a licensed water well drilling contractor.
While water well owners may legally disinfect their own wells, they should have a working knowledge of water system construction and be aware of electrical hazards before attempting such work.
Improper action could damage the water system or result in injury or death.