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."
Researchers have found that exposing it to ultraviolet light at treatment plants or bringing the water to a rolling boil for one minute seems to be effective. The EPA's proposed rule should be published in its final form this summer, Mr. King says.
But the list of emerging pollutants continues to grow as scientists conduct new tests. The US Geological Survey (USGS) released a study in 2002 on 95 organic contaminants such as prescription drugs and detergent byproducts that it looked for in US surface waters. The group tested 139 streams located downstream from major cities or animal feeding operations in 30 states and found 82 of the 95 chemicals on its list. No drinking-water standards or health-advisory requirements exist for many of the chemicals, whose effects have yet to be studied fully. The USGS will repeat and expand the study next year, and it hopes to release an updated report in early 2007, says Herb Buxton, coordinator of the USGS toxic substance hydrology program.
The USGS already has a list of more than 130 emerging contaminants that Mr. Buxton considers "sentinels" of potential environmental and human health effects. For example, Fluoxetine (Prozac), which has been found in waters in Britain and the US, can delay the development of fish. And substances that are thought to interfere with the body's hormone system and hinder fertility, known as endocrine disruptors, were found in treated wastewater and municipal drinking water in Atlanta in 1999.
"Finding these contaminants from households, animal agriculture, and industry makes us realize that the chemicals we use, even in very small amounts, can be concentrated in our wastewater and then deposited in streams that in turn are water resources," Buxton says.
While the effect of small amounts of pharmaceuticals, including antibiotics and antidepressants, in the water remains unknown, one researcher believes it could be relatively easy to remove some of them from drinking water with existing technologies. Water treatment operators could cut trace levels of drugs that get through sewage treatment systems by adjusting the amounts of activated charcoal and chlorine used to purify water now, says Craig Adams, a professor of environmental engineering at the University of Missouri-Rolla. Simply increasing the amount of activated charcoal can remove up to 90 percent of the drugs, he says.
The AWWA's Roberson says there is no magic bullet for drinking water contaminants. Thousands of potential contaminants are in the water, but the EPA has established drinking-water standards for only about 90 of them. The EPA is continuing to examine newly discovered pollutants to see if they need to be regulated. Local utilities also are required to test their water, usually once every three months, and every July they are required to send a water-quality report to homeowners. The reports are posted on the EPA's website (www.epa.gov/safewater/dwinfo.htm).
"Most people just throw the report away, but it can be incredibly useful," says Helen Rogan, executive editor at Organic Style magazine, which surveyed five contaminants in the water of 25 cities this past fall. She suggests that consumers who want to feel secure about their drinking water read the utility company's water report, have their tap water tested, and keep the EPA's Safe Drinking Water Hotline number handy (800-426-4791). The hotline also can suggest solutions (a filter, for example) if local water fails to meet federal standards.
"Your tap water is safe unless you have reason to believe otherwise," Ms. Rogan adds. "And if there is something wrong, you'll find out pretty fast."