Can safe water be defined?
Q:
Can safe water be defined?
A:
Safe water means water that will not harm you if you come in contact
with it. The most common use of this term applies to drinking water, but
it could also apply to water for swimming or other uses. To be safe,
the water must have sufficiently low concentrations of harmful
contaminants to avoid sickening people who use it. The list of harmful
contaminants includes disease-causing microbes such as bacteria,
viruses, and protozoans; cancer-causing chemicals such as many
pesticides, organic solvents, petroleum products, chlorinated byproducts
of the disinfection process, and some metals and metalloids; nitrates
and nutrients, endocrine-disrupting compounds, strong acids, strong
bases, radionuclides, and any other acutely toxic substance.
Defining
safe water becomes a matter of risk assessment, in which you consider
the chance of illness or injury from drinking the water, in comparison
to the risk of illness or injury from the many other hazards in our
lives,for example, riding in a car, or breathing the air, or shaking
hands, or exposure to radiation from the sun, or to contaminants in the
food we eat. In comparison to such other activities, drinking U.S.
public tap water, or any of the bottled waters, or water from most
domestic wells, is very safe indeed. These waters might come from wells
or springs that tap shallow or deep aquifers, from rivers or lakes, or
glaciers, or even from rain-water collectors, fog collectors, or from
desalinated sea water. Most of these waters are filtered and treated to
kill microbes and keep contaminants at safe levels.
How do you
define "safe levels"? The U.S. Environmental Protection Agency (EPA)
sets Maximum Contaminant Levels (MCLs) for many harmful contaminants,
based on health-effects research, contaminant occurrence data, economic
analysis, and risk analysis. The MCLs for currently regulated
drinking-water contaminants are listed on EPA's Office of Ground Water
and Drinking Water Web page under "Drinking water standards program."
Keep
this in mind: water that is safe for one person may be unsafe for
another. If your immune system is weakened by HIV/AIDS, or by a recent
bone-marrow transplant, or if you are a young child or an elderly
person, or pregnant or a nursing mother, you are more susceptible to
contaminants in drinking water than the rest of the population. Your
doctor may urge you to take extra precautions with the safety of your
drinking water. An online reference is EPA/CDC's guidance for people
with severely weakened immune systems is available. We can meet with you
and determine what you would need to meet your water quality needs.