How safe is the water?

A scare rippled through Washington, D.C., earlier this year when residents learned their drinking water contained lead, a metal linked to lower IQs in children and other maladies. The lead had leached into the water from aging pipes and fixtures. The city's water authority responded with a common remedy: It added a chemical called orthophosphate, which coats the inside of the pipes to contain the lead. But a month later, the city found the water contained elevated levels of bacteria, a side effect of the treatment.

Both the city and the US Environmental Protection Agency (EPA) assured residents the situation was not an emergency, and that the bacteria could be treated within months. Still, the city notified consumers of the situation and suggested that at-risk households, such as those with young children, seek medical advice.

So what should consumers believe about the safety of their drinking water?

Drinking water in the United States is among the best in the world - a United Nations study ranked it 12th among 122 countries. US water is treated and closely monitored so that isolated problems like the one in Washington, D.C., can be dealt with quickly. But scientists also are detecting for the first time substances - called "emerging pollutants" - that occur more routinely than had been thought. With new tests and technologies turning up these previously undetectable contaminants, a mixed picture is emerging of America's rivers, aquifers, and other freshwater sources that supply an estimated five out of six Americans.

What's disturbing is what's showing up in the water: industrial chemicals, human and veterinary drugs, feces, natural and synthetic hormones, microorganisms, detergents, and even fire retardants. Water companies do not yet test for most of these substances, and their effects on health and the environment are largely unknown.

These contaminants occur in such tiny amounts, however - at most, a drop of ink in the largest tanker truck - that so far most do not seem to pose a danger, scientists say. The mere fact that contaminants are being detected at these levels also means that the nation's water, already much cleaner than two generations ago, could be purified even more.

"I'm not too worried, because most occur at levels that are several orders of magnitude lower than a health concern," says Alan Roberson, director of regulatory affairs at the American Water Works Association (AWWA), a Washington, D.C. group of 57,000 water professionals.

"I drink water from the tap, and I'm comfortable," adds Ephraim King, director of the Standards and Risk Management Division of the EPA's Office of Water in Washington. "We've made pretty impressive progress in the last 25 to 50 years."

One example of that progress is cryptosporidium, a single-celled parasite that spreads when infected human or animal feces get into surface waters. It is relatively immune to chlorine, and its eggs can pass readily through most existing treatment plants. In 1993, it was linked to the largest recorded outbreak of a waterborne disease in US history, sickening 400,000 people and killing 50 in Milwaukee. From 1990 to 2000, at least 10 such outbreaks in the US were traced to impure water.

"Microbials are the problem we have been wrestling with the most over the past 10 years," says the AWWA's Mr. Roberson. "The EPA proposed a rule last year to require utilities to monitor source water for cryptosporidium, and if there are higher levels, then they have to put in additional treatment technologies to kill it or take it out."

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