Data compiled by a nationwide environmental organization is raising concerns when it comes to a certain kind of "radioactive" contaminant in Maryland's drinking water supply. Radium — the most common radioactive element found in tap water — was measured at levels above health guidelines in more than 200 Maryland water utilities, according to information released this month by the Environmental Working Group.

Radium is a naturally-occurring radioactive element that is found at low levels in all soil, water, and rocks. Radioactive elements enter groundwater from natural deposits in the earth's crust, but levels can be higher when uranium mining or oil and gas drilling unearth these elements from the rock and soil, the EWG explains. Exposure to radium over long periods of time can increase the risk of various types of cancer, and since radium "readily" accumulates in the body, it poses a greater cancer risk than most other radioactive elements, the USGS explains.

But it is important to note that health guidelines vary greatly from legal limits. The EPA's limit for radium-226 is 5 picocuries per liter. Health guidelines used in this report are based on public health goals set by the California Office of Environmental Hazard Assessment, which limits to 0.05 picocuries per liter. While California's public health goals are not legally enforceable limits, they are guidelines for levels of contaminants that pose only a minimal risk to health, the EWG explains. The EPA's standard, which has come under fire from environmentalists, was set in 1977 and was revised in 2000, according to a rule timeline posted to the EPA website.

Environmentalists, including those with the EWG, have taken issue with the EPA's standards. "Federal drinking water standards are based on the cost and feasibility of removing contaminants, not scientific determinations of what is necessary to fully protect human health," EWG said.

Even still, based on the more generous levels enforced by the EPA, advocates say water quality needs more scrutiny.

In Maryland, 104 utilities had water with radium-228 above accepted health guidelines, although they under EPA levels, plus 109 utilities with radium-226 levels that exceeded health limits. Nationwide, utilities in 27 states had radium levels above the legal limit.

You can explore the makeup of your water supply by visiting the EWG's Tap Water Database and putting in your ZIP code. The EWG says it mapped the nationwide occurrence of radium in tap water for almost 50,000 utilities. Between 2010 and 2015, the organization found that more than 22,000 utilities serving over 170 million people reported the presence of radium in their water at levels that may increase the risk of cancer.