Coliform Bacteria in Drinking Water - Fact Sheet

Coliform bacteria are a group of bacteria that are found in the intestines of humans and animals. These bacteria act only as indicators of possible fecal contamination because they can also be found in the soil. New Jersey State Drinking Water Standards require drinking water to be free of coliform bacteria. If a water supply is tested, coliform bacteria should be zero (0) [or less than 2.2 if an "MPN" [test is used].

If coliform bacteria is found in the water supply, it is the recommendation of this department that the well be chlorinated and then re-sampled for coliform bacteria. Instructions for chlorination are below. If the coliform bacteria persist, the well should be examined by a New Jersey licensed well driller. There are many reasons why coliform bacteria would occur in a well. The well could have a cracked or damaged casing or cap. The depth of the casing may be inadequate or the grouting around the well may be deficient.

Remediation may involve upgrading of the old well, the use of a well packer, or drilling of a replacement well that meets current standards. It is important to note that whenever work is done to a well or the water tank in the house, the well and the internal piping network in the house (see below) must be chlorinated in order to assure safe drinking water supply. If a well cannot be upgraded or a new well cannot be drilled because of restrictions on the property, then permanent disinfection can be used to eliminate the coliform bacteria problem.


Disinfection can be accomplished by the installation of a chlorination system, an Ultraviolet light treatment device or other available treatment systems. It should be noted that if the water is turbid, or if it contains traces of iron, the effectiveness of an Ultraviolet light treatment device is greatly reduced. In such cases, the water often needs to be filtered before it reaches the Ultraviolet light system. It is this department's recommendation that the well be shocked with chlorine and the internal pipes of the house are treated (see below) prior to the treatment system being installed. Until a permanent safe drinking water supply is available to you, follow these recommendations for a temporary safe drinking water supply:

Water used for drinking, for washing of vegetables to be eaten raw, making of ice, for brushing your teeth, and for preparation of cold beverages such as orange juice, should be from an alternate supply (e.g.: bottled water, jugs filled at a friend's house, etc.) or be disinfected.

You can disinfect your water supply by:

A. Boil the water at a full rolling boil for at least one minute, or

B. Chlorination with bleach (use six drops of bleach for each one gallon of water, let stand for 30 minutes).

Procedures for Chlorination of Potable Well

Disinfection is accomplished most effectively with a chlorine-containing chemical. Any common household liquid bleach that contains approximately five % "active" ingredient, usually sodium hypochlorite, is the most convenient chemical to use. The following table shows the proper amount of liquid bleach to be added directly to the well. All taps should be opened until chlorine odor is detected, and then held overnight or at least for several hours. The entire system should then be flushed out prior to reuse.

Note: All electrical power to the well pump should be shut off prior to removing the well cap.

A volume of 5 percent of bleach solution is required. (Disinfection strength approximately 50 parts per million).

Diameter of Well
Depth of Well

20'30'40'50'100' 200'
Up to 6"4oz6oz8oz10oz 20oz32oz
6" to 12"16oz24oz2 quart2 quart3 quart4 quart
12" to 24"2 quart 3 quart4 quart

24" to 48"2 gallon3 gallon4 gallon

Note: Liquid ounces.  32 ounces is 1 quart. A standard measuring cup is 8 ounces.