Today’s question: Is water that meets government drinking water standards absolutely safe?

"Plain Talk" answer: Safety is relative, not absolute. For example, an aspirin or two may help a headache, but if you took a whole bottle at once, you'd probably die. So, is aspirin safe? When setting drinking water standards, regulatory agencies use the concept of reasonable risk, not risk-free. Risk-free water is not technologically feasible and would cost too much. So the answer to the question is no, drinking water isn't absolutely safe. But the likelihood of getting sick from drinking water that meets the federal standards is very small, typically one chance in a million.

One difficulty federal agencies have when trying to determine reasonable risk relates to people who are more likely to get sick than others, called the susceptible population. For example, only babies three months old or younger are seriously affected by nitrates in drinking water, so for that contaminant they are the susceptible population. The standard for nitrate in drinking water, therefore, was chosen to protect infants. With other contaminants, identifying the susceptible population is not as easy. Are they babies, elderly, undergoing cancer treatment, in nursing homes, HIV positive, or others? For each standard, the federal regulatory agencies must balance the risk to all these groups against the cost of treatment and arrive at a standard that will protect as many people as possible at an affordable cost. This is called "the greatest good for the greatest number."

For more information on this and many other water-related topics, check out "Plain Talk About Drinking Water" by Dr. James M. Symons.