Photo of a water chlorinatorHazards of Chlorine in Drinking Water
Carcinogens & cancer risk? Other Health hazards?

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Drinking water disinfection byproduct (DBPs) hazards:

At what level and under what conditions is chlorinated drinking water or water treated with other disinfectants water a health hazard or a possible cancer hazard? Does chlorinated drinking water harm the septic tank?

This article answers questions about the harmfulness of chlorinated drinking water being discharged into the septic system. We explain that actual chlorine is not present in drinking water, that bleach is not "chlorine", and we describe potential health hazards associated with these substances.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Is my chlorinator or chlorinated water going into a private septic system likely to harm the septic tank or drainfield? Do some septic systems require chlorine or other disinfectants? Will chlorine, bleach, or Clorox™ damage the septic tank or leach fields? This document explains how to extend the life of the septic system by being careful about what goes into it.

Is There Actual Chlorine in Drinking Water? What health hazards are associated with chlorinated drinking water, chlorine, & bleach
Health Concerns, Remedies, Alternatives

Possible health risks from chlorinated drinking water

Water treated with chlorine for the purposes of disinfection may have handled a bacterial contamination worry but the chlorinated drinking water may still involve other health risks. [1]

Simpson (2008) found that or some waters, chloroacetic acid and chloral hydrate are the DBPs most likely to exceed the 1996 NHMRC Australian Drinking Water Guidelines:

Disinfection of water supplies is of paramount importance for the prevention of waterborne diseases. Unfortunately, an unwanted side effect is the formation of by-products. Currently, chlorine and monochloramine are the only agents used to disinfect major drinking water supplies in Australia. Historically, some Australian waters have produced high concentrations of disinfection by-products (DBPs) upon chlorination. However, most water authorities in Australia do not routinely monitor DBP concentrations, with only a few analysing for THMs alone. Accordingly, there has been very little information available on the nature, distribution and typical concentrations of DBPs in Australian drinking waters.

A number of analytical methods for the determination of DBPs were assessed and an analytical survey of 16 drinking waters from around Australia was conducted to determine their occurrence. Typically, DBP concentrations, with the exception of cyanogen chloride, were lowest in chloraminated waters. The survey revealed that for some waters, chloroacetic acid and chloral hydrate are the DBPs most likely to exceed the 1996 NHMRC Australian Drinking Water Guidelines. - Simpson (2008)

Nieuwenhuijsen (2000) notes:

Chlorination has been the major disinfectant process for domestic drinking water for many years. Concern about the potential health effects of the byproducts of chlorination has prompted the investigation of the possible association between exposure to these byproducts and incidence of human cancer, and more recently, with adverse reproductive outcomes.

These authors point out that while there are important questions to answer, research to date has been limited. Nevertheless caution is in order.

Relatively few toxicological and epidemiological studies have been carried out examining the effects of DBPs on reproductive health outcomes. The main outcomes of interest so far have been low birth weight, preterm delivery, spontaneous abortions, stillbirth, and birth defects— in particular central nervous system, major cardiac defects, oral cleft, and respiratory, and neural tube defects.

Various toxicological and epidemiological studies point towards an association between trihalomethanes (THMs), one of the main DBPs and marker for total DBP load, and (low) birth weight, although the evidence is not conclusive.

Administered doses in toxicological studies have been high and even though epidemiological studies have mostly shown excess risks, these were often not significant and the assessment of exposure was often limited. Some studies have shown associations for DBPs and other outcomes such as spontaneous abortions, stillbirth and birth defects, and although the evidence for these associations is weaker it is gaining weight. There is no evidence for an association between THMs and preterm delivery.

The main limitation of most studies so far has been the relatively crude methodology, in particular for assessment of exposure. - Nieuwenhuijsen (2000)

Batterman (2000) discuss the reactions between chlorine disinfectants, dissolved organics, and other chemicals in water to produce harmful disinfectin byproducts (DBPs) and on methods to reduce the level of DBPs using a mixed-disinfectant approach:

Reactions between chlorine disinfectants, dissolved organic matter, and other chemicals in water form a series of disinfection by-products (DBPs), including trihalomethanes (THMs) and haloacetic acids (HAAs), that are toxic and subject to increasingly stringent regulations. This paper explores effects on DBP formation produced by an alternative, non-chlorine-based secondary disinfectant comprised of silver and hydrogen peroxide (Ag+/H202) that is designed to provide long-lasting residual disinfection.

Based on a series of laboratory experiments using simulated treatment and distribution systems, post-chlorination additions of the secondary disinfectant dramatically reduced the formation of halogenated DBPs. Five source waters were tested over a range of conditions, including various levels of chlorine dosing, bromine and organic carbon concentrations, pH and temperature. For surface and ground waters, DBP reductions at 24 h with the secondary disinfectant averaged 72±9% for THMs and 67±11% for HAAs after a 10-min chlorination period. The dramatic reduction in halogenated DBPs occurred for all tested source waters and all disinfection conditions. The likely mechanism is the reduction of chlorine to chloride by H202, which halts further reaction of chlorine with dissolved organic matter and other DBP precursors. Thus, H202 acts as a quenching agent, in addition to its residual disinfectant properties in combination with Ag+.

This research shows a potential benefit of mixed disinfectants that provide a potentially viable option for controlling the formation of DBPs while maintaining effective disinfection. - Batterman (2000)

How to remove chlorine from drinking water

Clarification: chlorine is not present in "chlorinated water"

Chlorine is a gas with a very irritating odor. It is used in the production of thousands of products. It is also used for water disinfection, although the chlorine itself is quickly transformed into other chemicals at the beginning of the process.

Chlorine is not present in chlorinated water. During water chlorination, chlorine gas may be added to the water at first; however, the chlorine is quickly transformed into other chemicals (hypochlorous acid and hypochlorite anion), which actually disinfect the water.

The term ''free chlorine'' in drinking water usually refers to the amount of hypochlorous acid and hypochlorite in the water. It is important to recognize that these compounds are different from chlorine.

Chlorine is used to make bleach; bleach is not the same as chlorine.

Chlorine is broken down by sunlight within a matter of several minutes.

Chlorine dissolves in water and is converted into chloride and hypochlorous acid. . - "Chlorine toxicity", ATSDR [2]

Traditional methods to remove excess chlorine from drinking water use activated charcoal filtering. Because chlorine is volatile, you will also find that leaving water in an open pitcher or container will result in the dissipation of chlorine from that water quantity.

CHLORINE IN DRINKING WATER - Water Chlorinators and Septic Systems

Details about the effects of chlorine in septic systems, tanks, and drainfields are provided at CHLORINE IN SEPTIC WASTEWATER. Excerpts are below.

Using a chlorinator on well water: At homes where the water supply is not potable due to bacterial contamination, a common temporary solution is the installation of a chlorinator.

Often this consists of an injector which doses incoming water with chlorine, a holding tank to give the chlorine time to work, and a post-processing charcoal filter to remove the chlorine from the water. It's preferable to LARGER VIEW of
a home photo lab - lots of photo chemicals into the septic system might be a problem at this property

In a properly-operating chlorinator the level of chlorine in the house drinking water will not harm the septic system.

High levels of chlorine, such as from an improperly adjusted or malfunctioning chlorinator would be a problem for the occupants who would not want to be drinking such water, and might be a problem for the septic system too.

According to the US EPA, the effects of exceeding this chlorine limit in drinking water include the following:

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. [1]

It's easy to test for the level of chlorine in water - there are several inexpensive test kits suitable for homeowner use. For some suggestions on how to test the level of chlorine in drinking water see How to Test the Water Supply or Septic Effluent for Evidence of Chlorine (part of our article on cheating on water tests)

Photo of a UV light water sterilizer - ughUV (ultra violet) lights [photo] which are sold to treat bacterial contamination in water do not place any chemical into the water supply.

However if drinking water is contaminated with bacteria, a UV light is a not necessarily the best solution as other drinking water contaminants may be present too.

For a discussion of what happens when people dump chlorine into a well see

For a discussion of the effects of other water purification methods see DRINKING WATER EMERGENCY PURIFICATION and WATER DISINFECTION LIMITATIONS

Chloramine, Chlorine and Chlorine Dioxide Health Effects

Drinking Water Disinfection By-Products (DBPbs) & Their Hazards

Disinfectant Common Uses Health Effects of Disinfectant in Drinking Water Maximum residual disinfectant levels (MRDLs)
Chloramine (as Cl2) Chloramine is a water additive used to control microbes ... as a residual disinfectant in drinking water distribution system pipes. Drinking water with excessive levels of chloramine above the maximum residual disinfectant level (MRDL) could experience irritating effects to the eyes and nose, stomach discomfort or anemia MRDL = 4.0 mg/L or 4 ppm as an annual average
Chlorine (as Cl2) A ga or liquid form of chlorine (CL2) chlorine is used by municipal water systems to control microbes.

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.

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 containingchlorine dioxide well in excess of the MRDL for many years may experience anemia.

MRDL = 0.8 mg/L or 800 ppb


(Hypochlorite solution)


Health hazards from bleach:

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.

Cancer risk from chlorine? The Department of Health and Human Services (DHHS) the International Agency for Research on Cancer (IARC), and the Environmental Protection Agency (EPA) have not classified chlorine as to its human carcinogenicity

  • Bladder cancer risks: Cantor (2008)
  • "Chlorine toxicity", ATSDR [2]


The above information is adapted from US EPA, "Water: Basic Information about Regulated Drinking Water Contaminants", retrieved 8/27/2013, original source [1]

Ölmez proposes Chlorine dioxide, ozone, organic acids, peroxyacetic acid, electrolyzed oxidizing water and hydrogen peroxide for produce disinfection. These options are discussed at VEGETABLE DISINFECTION.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review, content suggestions, critique are welcomed and are listed at "References."


Continue reading at CHLORINE SOURCES in WATER or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see CHLORINATION WELL SHOCKING PROCEDURE as a common source of chlorine in both drinking water and septic systems.





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