Disinfection Byproducts: A Reference Resource
Disinfection byproducts are formed when disinfectants used
in water treatment plants react with bromide and/or natural organic matter (i.e., decaying vegetation)
present in the source water. Different disinfectants produce different types or amounts of
disinfection byproducts. Disinfection byproducts for which regulations have been established
have been identified in drinking water, including trihalomethanes, haloacetic acids, bromate, and
chlorite.
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Trihalomethanes (THM) are a group of four chemicals that are
formed along with other disinfection byproducts when chlorine or other disinfectants used to
control microbial contaminants in drinking water react with naturally occurring organic and
inorganic matter in water. The trihalomethanes are chloroform, bromodichloromethane,
dibromochloromethane, and bromoform. EPA has published the
Stage 1 Disinfectants/Disinfection Byproducts Rule
to regulate total trihalomethanes (TTHM) at a maximum allowable annual average level
of 80 parts per billion. This standard
will replace the current standard of a maximum allowable annual average level of 100 parts per
billion in December 2001 for large surface water public
water systems. The standard will become effective for the first time in December 2003 for small
surface water and all ground water systems.
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Haloacetic Acids (HAA5) are a group of chemicals that are
formed along with other disinfection byproducts when chlorine or other disinfectants used to
control microbial contaminants in drinking water react with naturally occurring organic and
inorganic matter in water. The regulated haloacetic acids, known as HAA5,
are: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and
dibromoacetic acid. EPA has published the
Stage 1 Disinfectants/Disinfection Byproducts Rule to regulate HAA5 at
60 parts per billion annual average.
This standard will become effective for large surface water
public water systems in
December 2001 and for small surface water and all ground water public water systems in December 2003.
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Bromate is a chemical that
is formed when ozone used to disinfect drinking water reacts with naturally
occurring bromide found in source water. EPA has established the
Stage 1 Disinfectants/Disinfection Byproducts
Rule to regulate bromate at annual average of 10
parts per billion in drinking water. This standard will become effective for
large public water
systems by December 2001 and for small surface water and all ground public
water systems in December 2003.
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Chlorite is a byproduct formed when chlorine dioxide is used
to disinfect water. EPA has published the Stage 1
Disinfectants/Disinfection Byproducts Rule to regulate chlorite at a monthly average level
of 1 part per million in drinking water. This standard will become effective for large surface water
public water systems in
December 2001 and for small surface water and all ground water public water systems in December 2003.
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