What is Cryptosporidium?

Cryptosporidium is a microscopic parasite commonly found in lakes and rivers, which is highly resistant to disinfection and can cause gastrointestinal problems. This microorganism can potentially cause gastrointestinal problems, particularly in those with severely weakened immune systems. This parasite is found in every region of the United States and throughout the world, according to the Centers for Disease Control and Prevention.

The parasite lives in bowel movements (stool, diarrhea) from infected people and animals.

  • It spreads through water—The parasite can live in drinking water or swimming pools. People can get infected when they swallow water with the parasite.
  • People with the infection can spread it if they do not wash their hands after a bowel movement/ using the bathroom. You can get sick if you touch an infected person or change an infected baby's diaper and then not washing your hands afterward.

A frequently asked questions (FAQ) document is available on the DPW website. This document answers essential health questions and explains steps that DPW is taking to protect the water supply.

Baltimore Water Quality

Weekly sampling from Druid Lake reservoir has shown no additional detections of cryptosporidium. However, a sample collected from Druid Lake reservoir on September 19, 2023, tested positive for the organism. The water remains safe for the general public to consume. Nevertheless, out of an abundance of caution, the Maryland Department of Health and the Maryland Department of the Environment advise people with severely weakened immune systems to continue to take the following precautions:

  • Drink bottled water, OR
  • Boil water for one minute before consuming, OR
  • 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)

Public Health Coordination

DPW continues to collaborate with the Maryland Department of the Environment (MDE), U.S. Environmental Protection Agency (EPA), the Maryland Department of Health, and the Baltimore City Health Department (BCHD) on public notification guidelines and to ensure that the message of water safety is communicated to the public.

Public Notification

DPW will continue to notify the public of all detections through press releases to local media, social media posts, email notifications, and other avenues. DPW will also continue coordinating with the BCHD to reach facilities that serve people at higher risk of more severe disease.

Covering Druid Lake and Ashburton Reservoirs

DPW is in the process of covering the two remaining uncovered treated drinking water reservoirs, Ashburton and Druid Lake, in the City of Baltimore’s water system. These uncovered reservoirs hold filtered and treated water ready to be delivered to customers.

Work is scheduled to be completed on Druid Lake on Dec. 30, 2023, and on Ashburton on Nov. 30, 2023, in compliance with the timeline agreed on by the City and U.S. Environmental Protection Agency (EPA), under a modified Administrative Order of Consent.

At Ashburton and Druid Lake, DPW is working to build massive underground tanks to protect its water supply. Completing these projects will add safeguards to the City’s treated drinking water supply from Cryptosporidium and other contaminants.

Source Water Protection and Monitoring

DPW routinely monitors its source water locations for Cryptosporidium, and these results appear in DPW’s annual water quality reports. State and federal guidelines address reporting and monitoring for Cryptosporidium at source water locations. No such guidelines exist for monitoring Cryptosporidium in water that has been filtered and treated

Monitoring results included in DPW’s most recent Water Quality Report indicate that the source water is not affected by Cryptosporidium. Source water is obtained from the Liberty and Loch Raven reservoirs and the Susquehanna River during drought conditions that contribute 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.

Source Water Cryptosporidium Results-2022
Liberty: 0.0 - 0.09 Oocyst/Liter
Loch Raven: 0.0 – 0.09 Oocyst/Liter
Susquehanna River: 0.00 – 0.36 Oocyst/Liter

Druid Lake, Ashburton Test Results

DPW tests water at the Ashburton and Druid Lake finished reservoirs as part of a recently modified Administrative Order on Consent between the City of Baltimore and the U.S. Environmental Protection Agency (EPA). This order requires sampling for Cryptosporidium and Giardia at the City’s uncovered finished reservoirs.

DPW has committed to sampling for Cryptosporidium and Giardia at the Ashburton and Druid Lake Reservoirs every week. Each of these test results will be posted on this webpage.

Druid Lake – December 18, 2023

Druid Lake – December 11, 2023

Ashburton/Druid Lake – December 4, 2023 Ashburton/Druid Lake – November 27, 2023 Ashburton/Druid Lake – November 20, 2023 Ashburton/Druid Lake – November 13, 2023 Ashburton/Druid Lake – November 6, 2023 Ashburton/Druid Lake – October 30, 2023 Druid Lake, Ashburton – October 23, 2023 Ashburton/Druid Lake - October 16, 2023 Ashburton/Druid Lake - October 10, 2023 Ashburton/Druid Lake - October 3, 2023
Druid Lake - September 27, 2023
Ashburton/Druid Lake – September 19, 2023 (0.09 Cryptosporidium Oocyst/Liter)
Ashburton/Druid Lake – August 21, 2023
Ashburton/Druid Lake - July 24, 2023