A water sample collected Tuesday from the Druid Lake Reservoir was found clear of the parasite cryptosporidium, marking the second negative test result since authorities last week advised some customers to boil their water.

Baltimore City’s Department of Public Works first discovered low levels of cryptosporidium, or crypto, in the region’s drinking water last week. The parasite was detected in Druid Lake Reservoir — an open-air reservoir that supplies drinking water for parts of Baltimore City and Baltimore County, as well as Howard County — following routine testing of a sample collected on Sept. 19. The results were reported from an outside lab a week later, on Sept. 26.

The test result from the sample collected Tuesday was expedited, said department spokeswoman Jennifer Combs in an email. The department previously told The Banner that one week was the quickest time frame its lab, Analytical Services Inc., could offer.

Although crypto is not considered a serious risk for healthy people, it can cause infection and other gastrointestinal issues for older people, children and those with compromised immune systems.

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The Maryland Department of Health on Tuesday continued to advise vulnerable people who get their water from the Druid Lake Reservoir to boil water for one minute before consuming, drink bottled water, or treat the water with a filter designed to remove particles one micron or larger.

Druid Lake Reservoir is one of the city’s two uncovered drinking water reservoirs still out of compliance with the federal Safe Drinking Water Act (the other is Ashburton). Baltimore City was ordered in 2010 to bring its water sources into compliance as part of a federal consent decree issued by the Environmental Protection Agency.

Federal authorities say uncovered water supplies are vulnerable to contamination from birds and insects. Baltimore is working toward compliance by installing tanks to replace the two uncovered reservoirs. However, the project has experienced “delays due to unforgiving site conditions, weather delays, supply and worker shortages caused by the COVID 19 pandemic, supply chain delays etc.,” Combs told The Banner this month.

In the meantime, the federal order requires the city to conduct monthly monitoring and sampling of the Druid Lake and Ashburton reservoirs. Source water is treated for crypto before the water ends up in Druid Lake.

lillian.reed@thebaltimorebanner.com