No traces of the parasite cryptosporidium were found in a water sample taken from the Druid Lake Reservoir, the Baltimore City Department of Public Works said Tuesday.

The clean bill of health came five days after the department said it had discovered low levels of cryptosporidium, or crypto, in the open-air reservoir that supplies drinking water for parts of Baltimore City and Baltimore County, as well as Howard County.

The finding amounted to a low risk for the general population, although the parasite can cause gastrointestinal problems for older people, children and those with compromised immune systems.

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.

Uncovered reservoirs like Druid Lake are vulnerable to contamination from birds and insects. DPW is working to build underground tanks to protect the treated water supply at the Druid Lake and Ashburton reservoirs. It expects those improvements to be completed by the end of 2023. Meanwhile, it will continue testing water samples for cryptosporidium and giardia at both reservoirs on a weekly basis and post results on its website.

The initial cause of concern came from a routine monthly test on a water sample taken Sept. 19, with the results reported from an outside lab a week later, on Sept. 26. Scientists and laboratory managers told The Baltimore Banner that the parasite can be identified by lab testing in as little as 24 hours, but DPW officials had said they were at the mercy of the lab’s processing time.

Cryptosporidium is a parasite found in water that can cause an infection called cryptosporidiosis, which can lead to diarrhea and other gastrointestinal issues but “is normally not a serious disease in healthy people,” according to Johns Hopkins Medicine.

City officials said that because the level of crypto detected last week was so low, it was not possible to precisely determine the source of the parasite, although it did not come from Druid Lake’s source water (the Liberty, Loch Raven and Prettyboy reservoirs). As part of its regular filtration process, the source water is treated for crypto before the water ends up in Druid Lake.

Under a federal consent decree issued by the Environmental Protection Agency, which the city has been under since 2010, Baltimore must bring its five uncovered drinking water reservoirs into compliance with the federal Safe Drinking Water Act. Druid Lake and Ashburton are the only two reservoirs not yet in compliance.

The delayed projects “have been subject to unavoidable and extensive delays due to unforgiving site conditions, weather delays, supply and worker shortages caused by the COVID 19 pandemic, supply chain delays etc.,” DPW spokeswoman Jennifer Combs wrote in an email to The Banner.

hugo.kugiya@thebaltimorebanner.com