As officials clear more West Virginians to drink their tap water, the Center For Disease Control advised pregnant women living near the site of a chemical spill to continue using bottled water.

A notice posted by the West Virginia Department of Health and Human Resources said “out of an abundance of caution,” women should avoid drinking the water “until there are no longer detectable levels of MCHM [or 4-Methylcyclohexanemethanol] in the water distribution system.”

The advisory continues, “However, the CDC re-affirmed previous advice that it does not anticipate any adverse health effects from levels less than one part per million.”

West Virginia American Water has gradually lifted over three days a “do-not-use” order for the area surrounding the spill site. As of Thursday, officials cleared two-thirds of affected customers to drink their tap water.

Little is known about MCHM, the chemical leaked into the Elk River by the thousands of gallons at a site managed by Freedom Industries, Inc. In the days since the spill, it’s been revealed that no one has conducted human health studies on MCHM. The chemical was one of 64,000 grandfathered in with the Toxic Substances Control Act, meaning no one is required to test its safety before use.

The CDC’s advisory has heightened skepticism of West Virginia’s water safety claims. ABC reports:

[Jennifer] Kayrouz, who has a 6-year-old daughter, and other pregnant women, along with some health care providers, wondered why the CDC delayed its warning and whether pregnant women living in affected counties had been lured in to a false sense of security that the tap water was safe.

“If it is not safe for me to drink pregnant, is it safe for my 55-pound daughter to drink or our pets?” Kayrouz asked. “It’s very misleading. We got the green light, and three days later were told this one population really shouldn’t drink it.”

Brandy Russell, community director for the West Virginia March of Dimes, which fights against birth defects, said, “Everyone is freaking out,” and not just pregnant women.

She said there had been an uptick of calls to its Charleston office over the past weekend. And since the ban was lifted, residents continue to express worry.

After officials lifted the “do-not-use” order, emergency rooms reported an influx of patients with symptoms related to exposure to chemical-tainted water.