A new analysis showing the presence of a probable carcinogen in the tap water of 31 cities across the country has raised questions about possible risks posed to consumers in those communities and how they can reduce their exposure.

The chemical, hexavalent chromium, got public attention in the 2000 film "Erin Brockovich" and has been found to cause cancer in laboratory animals by the National Toxicology Program, part of the National Institutes of Health.

Although basic water filters such as those made by Brita and PUR do not remove hexavalent chromium, several reverse-osmosis systems designed for home use can take the chemical out of water. Such systems are available for purchase online and at hardware stores.

Bottled water is not necessarily an alternative because it is often drawn from municipal water systems and can still contain hexavalent chromium or other contaminants.

The analysis, released Monday by the Environmental Working Group, is the first nationwide look at hexavalent chromium in drinking water to be made public. The advocacy group sampled tap water from 35 cities and detected hexavalent chromium in 31 of those communities. Of those, 25 had levels that were higher than a health goal proposed last year by the state of California.

Locally, Bethesda and Washington had levels of .19 parts per billion, more than three times the California goal.

The federal government has not set a limit for hexavalent chromium in drinking water but is reexamining the chemical to decide whether it should impose such restrictions.

"This definitely raises the issue about a national drinking water standard for hexavalent chromium and why we don't have one," said Lynn Goldman, an epidemiologist and former top official at the Environmental Protection Agency who now serves as dean of the School of Public Health at George Washington University.

Goldman said the new study demands deeper investigation. "This is the very first signal that there might be a problem," she said. "But it's premature to say we know really what the level (of contamination) is, whether it's there all the time or just intermittently and what the source is."

Illinois senators Richard Durbin (D) and Mark Kirk (R) planned to meet Tuesday with EPA Administrator Lisa Jackson to discuss the report, which found hexavalent chromium in Chicago drinking water at about the same levels as in Bethesda and Washington.

Last year, California released a draft of a "public health goal" for a safe level of hexavalent chromium in drinking water: 0.06 parts per billion. If the state sets a limit, it would be the first in the nation.

Hexavalent chromium was a commonly used industrial chemical until the early 1990s. It is still used in some industries, such as chrome plating and the manufacturing of plastics and dyes. The chemical can also leach into groundwater from natural ores.