Water Pollution - The Drinking Water - page 169

Public Health Concerns

Most Americans drink tap water that meets all existing health standards all
the time. These rules were designed to further strengthen existing drinking
water standards and thus increase protection for many water systems. The
USEPA's Science Advisory Board concluded in 1990 that exposure to microbial
contaminants such as bacteria, viruses, and protozoa (e.g., Giardia lamblia and
Cryptosporidium ) was likely the greatest remaining health risk management
challenge for drinking water suppliers. Acute health effects from exposure to
microbial pathogens are documented, and associated illness can range from
mild, to moderate cases lasting only a few days, to more severe infections
that can last several weeks and may result in death for those with weakened
immune systems. Disinfectants are effective in controlling many microorgan-
isms, but they react with natural organic and inorganic matter in source water
and distribution systems to form potential DBPs, many of which have been
shown to cause cancer and reproductive and developmental effects in labo-
ratory animals. More than 200 million people consume water that has been
disinfected. Because of the large population exposed, health risks associated
with DBPs, even if small, need to be taken seriously.

Existing Regulations

• Microbial contaminants —The 1989 Surface Water Treatment Rule
applies to all public water systems using surface water sources or
groundwater sources under the direct influence of surface water. It
establishes maximum contaminant level goals (MCLGs) for viruses,
bacteria, and Giardia lamblia . It also addresses treatment tech-
nique requirements for filtered and unfiltered systems specifically
designed to protect against the adverse health effects of exposure
to these microbial pathogens. The Total Coliform Rule, revised in
1989, applies to all public water systems and establishes a maximum
contaminant level (MCL) for total coliforms.
• Disinfection byproducts —In 1979, the USEPA set an interim MCL for
total trihalomethanes of 0.10 mg/L as an annual average. This applies
to any community water system serving at least 10,000 people that
adds a disinfectant to the drinking water during any part of the treat-
ment process. In 1998, the USEPA established the Stage 1 Disinfectants
and Disinfection Byproducts Rule, which required public water sys-
tems to use treatment measures to reduce the formation of disinfec-
tion byproducts and to meet the following specific standards:
Disinfection byproducts Treatment standard

Total trihalomethanes 80 ppb

Haloacetic acids 60 ppb

Bromate 10 ppb

Chlorite 1 ppm