Well depths and types (C) Carson Dunlop Associates Well disinfectant choices
Comparison of common water well disinfectants & their properties

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Well disinfectant chemicals & their properties: this article describes the properties of three most common disinfectants used to shock or sanitize a water well: chlorine (common household bleach), chloramine, and chlorine dioxide.

Page top sketch illustrating both deep and shallow water well construction and depths is provided courtesy of Carson Dunlop Associates.

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Comparison of the 3 Common Well Water Disinfectants: Chloramine, Chlorine and Chlorine Dioxide

Chloramine, Chlorine and Chlorine Dioxide Used for Well Shocking / Disinfection Procedures

Disinfectant Common Usages Health Effects Comments
Chloramine (as Cl2)

Chloramine is a water additive used to control microbes ... as a residual disinfectant in drinking water distribution system pipes.

Chloramine is formed when ammonia is added to water containing free chlorine. Monochloramine is a form of chloramine commonly used for disinfection by municipal water systems

Drinking water with excessive levels of chloramine above the maximum residual disinfectant level (MRDL) could experience irritating effects to their eyes and nose, stomach discomfort or anemia MRDL = 4.0 mg/L or 4 ppm as an annual average
Chlorine (as Cl2)

As a gaseous or liquid form of chlorine (CL2) chlorine is a powerful oxidant used by municipal water systems to control microbes.

Chlorine is relatively inexpensive and has the lowest production and operating costs and longest history for large continuous disinfection operations.

Some people who use water containing chlorine well in excess of the maximum residual disinfectant level could experience irritating effects to their eyes and nose.

Some people who drink water containing chlorine well in excess of the maximum residual disinfectant level could experience stomach discomfort.

MRDL = 4.0 mg/L or 4 ppm as an annual average
Chlorine dioxide (as ClO2) Chlorine dioxide is added to water to control microbes and can be used to control tastes and odors. Highly volatile, chlorine dioxide rapidly disappears from stored water.

Some infants, young children, and fetuses of pregnant women who drink water containing chlorine dioxide in excess of the maximum residual disinfectant level could experience nervous system effects

. Some people who drink water containing chlorine dioxide well in excess of the MRDL for many years may experience anemia.

MRDL = 0.8 mg/L or 800 ppb
Household Bleach e.g. Clorox® contents & purposes of each chemical


  1. Sodium hypochlorite (NaClO)
  2. Sodium chloride (NaCl)
  3. Sodium carbonate (Na2CO3)
  4. Sodium chlorate (NaClO3)
  5. Sodium hydroxide (NaOH)
  6. Sodium polyacrylate (C3H3NaO2)n
  7. Water (H2O)
  1. In Clorox's EPA-registered disinfecting and sanitizing products, sodium hypochlorite is the active ingredient that helps to kill certain germs. This is the principal ingredient in household bleach.
  2. Sodium chloride (table salt) is used as a thickener in some products.
  3. Sodium carbonate (washing soda) is an alkalinity builder that boosts the cleaning power of laundry detergents
  4. Sodium chlorate is an intermediate product in the break-down of standard bleach (sodium hypochlorite); it further breaks down into sodium chloride (salt) and oxygen.
  5. Sodium hydroxide (lye, caustic soda) is used to adjust the pH of cleaners and to assist in breakdown of fats & oils
  6. Sodium polyacrylate helps keep soils suspended during washing to avoid re depositing them on fabrics being cleaned.

According to the US ATSDR's fact sheet on chlorine:

Watch out: Drinking small amounts of hypochlorite solution (less than a cup) can produce irritation of the esophagus.

Drinking concentrated hypochlorite solution can produce severe damage to the upper digestive tract and even death. These effects are most likely caused by the caustic nature of the hypochlorite solution and not from exposure to molecular chlorine.

Spilling hypochlorite solution on the skin can produce irritation. The severity of the effects depends on the concentration of sodium hypochlorite in the bleach.

Adapted from clorox.com

For emergency disinfection of drinking water (his is NOT the same thing as disinfecting a well) add 8 drops of Clorox bleach to a gallon of clear water, (or just two drops to a quart) and let the solution stand for at least 15 minutes (a very slight "bleach" odor should remain.

If there is no bleach odor the water may not be adequately disinfected.





The above information is adapted from US EPA, Water: Basic Information about Regulated Drinking Water Contaminants, retrieved 8/27/2013, original source water.epa.gov/drink/contaminants/basicinformation/disinfectants.cfm [1]
and from information provided by clorox.com

Watch out: The US EPA recommends that you test your water every year for total coliform bacteria, nitrates, total
dissolved solids, and pH levels.

If a review of local well water contaminants found by local testing labs, your local health department, or other information about your particular property suggests that there is a risk of other chemical contaminants (such as agricultural chemicals, pesticides, or local chemical spills or dumps) then you should include a test for these contaminants as well.

For problem wells whose contamination is not easily cured by the above, see WELL DISINFECTANT TABLE, POST FLOODING


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