DPW Detects Low Levels of Cryptosporidium During Routine Testing of Druid Lake Reservoir

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DPW Detects Low Levels of Cryptosporidium During Routine Testing of Druid Lake Reservoir

Today, the Baltimore City Department of Public Works (DPW) announced that during a routine test of the Druid Lake Reservoir low levels of the microscopic parasite Cryptosporidium were discovered. Cryptosporidium is a microorganism commonly found in lakes and rivers, which can potentially cause gastrointestinal problems, particularly, in those who are immunocompromised, elderly, or children.

This detection impacts only a portion of the Baltimore region water system, in Baltimore City, Baltimore County, and Howard County. The affected area is shown in the map below.

Please rest assured that our drinking water remains safe for the general population. This is not related, or in any way comparable, to previous water-related issues. Residents can use an Interactive Map to determine if they live in an impacted area.  


Map Photo

What is Cryptosporidium?

Cryptosporidium is a microscopic parasite that can be found in water sources. While it can cause health issues, it's important to emphasize that the levels detected in our water supply do not pose an immediate health risk to the general public. Cryptosporidium is extremely chlorine tolerant, like systems frequently used at hospitals, so secondary treatment is unlikely to reduce its levels.

What’s The Most Important Thing You Need to Know?

The levels of Cryptosporidium detected in our water supply indicate a low risk for the general population. This means that for most people, the water is still safe to drink. However, vulnerable populations should consider taking precautions.

Who should consider taking precautions and what precautions can be taken?

DPW has consulted with the Baltimore City Health Department, which has determined that due to the low-risk, most residents do not need to take any additional precautions unless they have an immunocompromising condition. Exposure to Cryptosporidium can cause cryptosporidiosis, symptoms can include diarrhea, vomiting, fever, and stomach pain. People with healthy immune systems typically are not impacted or quickly recover without medical treatment.

Examples of people with weakened immune systems include those with HIV/AIDS, those with inherited diseases that affect the immune system, cancer, and transplant patients who are taking certain immunosuppressive drugs.

Those with immunocompromising conditions and other sensitive populations are advised to:

  • Drink bottled water
  • Boil water for one minute before consuming
  • Filter tap water using a filter labeled to ANSI/NSF 53 or 58 standards, or a filter designed to remove objects 1 micron or larger. These may be labeled “absolute 1 micron.” (i.e., not Brita-type filters)

Why is testing required?

This test was conducted as part of DPW’s recently modified Administrative Order on Consent between the City of Baltimore and the U.S. Environmental Protection Agency (EPA), which stipulates sampling for Cryptosporidium and Giardia at the City’s uncovered finished reservoirs. Work on the two remaining uncovered finished reservoirs, Ashburton and Druid Lake Reservoir  is expected to be completed by November 30, 2023 and December 30, 2023, respectively.

Samples were collected on September 19, 2023, at the Druid Lake uncovered reservoir  and through testing 0.09 Cryptosporidium Oocyst/Liter was detected. The samples follow a thorough laboratory analysis and results are returned within seven days; the results for the test taken this month were returned on September 26, 2023. Monthly sampling collected at Druid Lake Reservoir in August showed no signs of Cryptosporidium.

Please note that the recent monitoring results indicated that the source water is not affected by Cryptosporidium. Source water is obtained from the Liberty, Loch Raven, and Prettyboy reservoirs, as well as the Susquehanna River during drought conditions that contributes to the City’s water supply. As part of the water filtration process, DPW treats source water for Cryptosporidium before it is delivered to the finished water reservoirs. This parasite is found in every region of the United States and throughout the world, according to the Centers for Disease Control and Prevention.

What happens next?

DPW will conduct more frequent sampling for Cryptosporidium at the City’s finished water reservoirs until sampling results can reliably show that Cryptosporidium is not detected.

DPW will notify the public and media on the results of those additional sampling tests.

Where Can I Find Additional Information?

Additional information can be found at the CDC Website here:





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