5
CWS - Acute vs. Chronic Indicators
The contaminants fall into two groups according to the health effects that they cause:
Graph 3 (below) shows that 98.6 percent of the population served by Illinois CWS received
drinking water in compliance with acute (short-term) health requirements, and 92.7 percent were
in compliance with chronic (long-term) health requirements. It is important to note that most non-compliance
was short in duration, and the potential for health risk was minimized through prompt
corrective action by the water supplies. Supplies with microbial problems (bacterial or turbidity
non-compliance) are required to issue boil orders when the violation occurs. Community water
system acute MCLs were limited to five water systems.
Acute and Chronic Requirements (2004 data)
Percent of CWS Population Served Compliant with Health Records
Acute effects occur within hours or days of the
time that a person consumes a contaminant.
People can suffer acute health effects from
almost any contaminant if they are exposed to
extraordinarily high levels (as in the case of a
spill). In drinking water, microbes, such as
bacteria and viruses, are the contaminants
with the greatest chance of reaching levels
high enough to cause acute health effects.
Most people’s bodies can fight off these
microbial contaminants the way they fight off
germs; and these acute contaminants typical-ly
don’t have permanent effects. Nonetheless,
when high enough levels occur, they can
make people ill, and can be dangerous or
deadly for a person whose immune system is
already weak due to HIV/AIDS, chemothera-py,
steroid use, or another reason.
Chronic effects occur after people consume a
contaminant at levels over EPA’s safety stan-dards
for many years. USEPA develops the
standards for chronic MCLs on the basis that
a person may have an adverse health effect
after consuming two liters of water daily over
a 70 year lifetime. The drinking water con-taminants
that can have chronic effects are
chemicals (such as disinfection by-products,
solvents, and pesticides), radionuclides (such
as radium), and minerals (such as arsenic).
Examples of the chronic effects of drinking
water contaminants are cancer, liver or kidney
problems, or reproductive difficulties.
Acute Chronic
• Graph 3
