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The Baltimore Banner, How safe is your water? Questions about cryptosporidium in Baltimore answered 

The Baltimore City Department of Public Works late last week announced low levels of the parasite cryptosporidium had been detected in Druid Lake Reservoir, an open-air reservoir that feeds into the water supply for parts of Baltimore City and Baltimore County, as well as Howard County.

The parasite is known to cause gastrointestinal issues, especially in older people, children and those with weakened immune systems. The department on Saturday said the detection advisory “remains in effect until further notice.” For most people, though, the water is safe. Here are some answers to commonly asked questions.
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The cryptosporidium was detected in the Druid Lake reservoir in a routine testing sample that was collected on Sept. 19, according to city officials, and laboratory results were reported on Sept. 26.

Druid Lake Reservoir, like the Lake Ashburton Reservoir, holds water that has already been treated for consumption. City officials said that because such a low level was detected, it is not possible to determine a source of the parasite. This past weekend, DPW said that recent monitoring indicates that source water — obtained from the Liberty, Loch Raven and Prettyboy reservoirs — is not affected by crypto. As part of its regular filtration process, DPW treats source water for crypto before the water is delivered to its finished reservoirs.

The water was tested again on Sept. 27, but officials said it could be another week before those results came back.

On Sept. 28, DPW publicly reported the presence of the parasite in the drinking water based on the Sept. 26 test result. In the update shared this past weekend, DPW did not explicitly say why it did not share the test results when the agency received them on Sept. 26.
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Update: 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 Oct. 3. 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.

Cryptosporidium is one of relatively few waterborne diseases that are resistant to chlorination, the standard form of water treatment. It is also difficult to filter out making it one of the more problematic.