After the discovery of cryptosporidium in Baltimore’s Druid Lake Reservoir last month, subsequent tests have come back negative.

Even so, immunocompromised people, who face potentially serious health consequences from cryptosporidium, were advised “out of an abundance of caution” to continue avoiding tap water.

The Baltimore Department of Public Works (DPW) pledged to conduct weekly testing for the health harming parasite and to make the results public.

But where?

While DPW hasn’t publicized it, the agency has begun posting the test results on its website at Reservoir-Testing.

(Hat tip to freelance science writer @AnnFinkbeiner, who shared on Twitter that she found the page “by accident” today.)

The latest results posted – for samples taken on Tuesday (October 10) – show no trace of cryptosporidium at Druid Lake or at the city’s other open-air reservoir, Lake Ashburton.

The weekly testing also monitors for the presence of another microscopic parasite, giardia. The October 10 samples were negative for giardia.

The analysis by Analytical Services, Inc., of Williston, Vermont was conducted on Thursday (October 12), according to the new webpage.

The findings were reported that day to Deneen Gordon, laboratory technical administrator at the Ashburton Filtration Plant.

The new page has other information of interest to water customers in the wake of the contamination, though no specific health advisory.

For that question, there’s a link to this DPW page, Cryptosporidium: Frequently Asked Questions.

Health Concerns

The initial finding of cryptosporidium in Druid Lake prompted widespread concern because the microscopic parasite can cause diarrhea, stomach cramps, vomiting and other gut and systemic symptoms.

Describing that first result of .09 oocysts per liter as “low level,” public works and health officials said it was safe for the general public to drink the water.

“Symptoms usually last about one to two weeks, with a range of a few days to four or more weeks, in persons with healthy immune systems,” according to the U.S. Centers for Disease Control and Prevention (CDC).

DPW advised people with weakened immune systems, such as cancer patients and people with HIV/AIDS, to boil or filter their tap water or drink bottled water.

Anyone can get sick from “crypto,” as it’s often called, but immunocompromised people are more likely to have severe and potentially life-threatening symptoms, the CDC says.

• Information for People With Weakened Immune Systems (CDC)

Special care should be taken to make sure that young children and the elderly who get the illness, cryptosporidiosis, do not become dehydrated, the federal health agency also warns.

Unprotected Water Sources

As The Brew has reported, Baltimore only began testing for cryptosporidium and giardia in July because it was ordered to do so by the Environmental Protection Agency.

• Ahead of cryptosporidium finding in Druid Lake, city was told repeatedly to end open-air drinking water storage (10/2/23)

• Q&A with DPW on cryptosporidium detected in Druid Lake (10/2/23)

The testing mandate was part of a crackdown after DPW missed multiple deadlines – across many years – to build underground tanks to store drinking water at Druid Lake and Lake Ashburton.

Currently, the open-air reservoirs are unprotected from contaminants and runoff.

DPW was told by EPA to finish the tank projects by the end of the year.

The agency says it’s on track to meet the latest deadlines: November 30 for Lake Ashburton and December 30 for Druid Lake.