Monitoring for Pathogens

Photo of a cryptosporidium oocyst, and a giardia cyst under a microscope
Cryptosporidium oocyst and Giardia cyst

We began monitoring for the protozoa Cryptosporidium and Giardia in 1992 as part of our comprehensive watershed monitoring program. Today, we analyze over 500 samples each year from nearly 50 sites, including the effluent of the Kensico Reservoir (Catskill/Delaware System) and the influent to the Croton Filtration Plant Croton System. These two sites are designated as New York City’s source water, which means that they are representative of the water prior to treatment including disinfection by chlorine and ultraviolet light. In addition to routine monitoring, we may occasionally collect protozoan samples in response to heavy rainfall or for research projects or other special investigations. For general drinking water monitoring information, visit Drinking Water Monitoring.

Pathogen Sampling Data

View the NYC OpenData: Cryptosporidium And Giardia Data Set

Waterborne Disease Risk Assessment Program

Our Waterborne Disease Risk Assessment Program documents and tracks rates of giardiasis and cryptosporidiosis, along with demographic and risk factor information on case patients.


Methods to collect water samples and analyze them for Cryptosporidium and Giardia have improved dramatically since 1992. Currently, we use the United States Environmental Protection Agency (EPA) approved Method 1623.1 to analyze samples. Prior to switching to new and improved methods, we conduct validation studies to demonstrate that new methods recommended by the EPA provide more accurate and consistent results. Since recoveries from one method to the next have improved, results from the different methods may not be comparable. For reference, our method history includes ASTM D-19 P229 from 1992 to 1998, EPA ICR method from 1999 to 2000, and EPA 1623 from October 2001 to 2015. Our current method, EPA Method 1623.1, was implemented in April 2015. This method provides significantly better recovery and identification of Giardia and Cryptosporidium. Our Pathogen Laboratory is approved by the State of New Hampshire to perform Method 1623.1 under the Laboratory Quality Assurance Evaluation Program for Analysis of Cryptosporidium in preparation of the Long-Term 2 Enhanced Surface Water Treatment Rule.

We work continually to improve our sample collection and analytical methods, but there are deficiencies with the current standard method. EPA 1623.1 is not intended to determine whether Cryptosporidium and Giardia found in water samples are dead, alive, or infectious. We are working with the University of Texas and others to develop and implement new analytical methods to identify the genotype of Cryptosporidium recovered from environmental samples and to provide information as to whether the types are human pathogenic or infectious. Results to date indicate that our environmental samples largely contain Cryptosporidium from wildlife sources, and are therefore unlikely to infect humans. While there are no numerical drinking water standards for Cryptosporidium and Giardia, the EPA implemented the Long-Term 2 Enhanced Surface Water Treatment Rule. Our monitoring results indicate that New York City’s source waters are below the treatment threshold required in the current regulations.

Illness from Cryptosporidium and Giardia

Cryptosporidium and Giardia are protozoa which cause the intestinal illnesses cryptosporidiosis and giardiasis, respectively. These diseases are transmitted by eating contaminated food, drinking contaminated water, swallowing contaminated water while swimming or bathing, having contact with animal or human feces, and certain sexual practices. Symptoms of infection include nausea, diarrhea, and abdominal cramps. Individuals who think they may have cryptosporidiosis or giardiasis should contact their health care providers. Visit the New York City Department of Health (giardiasis and cryptosporidiosis) or Center for Disease Control web pages (giardiasis and cryptosporidiosis) for more information on this topic.

Some people may be at greater risk from cryptosporidiosis and giardiasis than the general population. Immuno-compromised people, such as individuals undergoing chemotherapy; those who’ve undergone organ transplants or dialysis; and those with HIV/AIDS or other immune system disorders, can be at increased risk. These people should seek advice from their health care providers about taking steps to limit their exposure to the protozoa that cause infection. Steps and guidelines on appropriate means to lessen the risk of infection by Cryptosporidium and other microbial contaminants via drinking water are available from the EPA’s Safe Drinking Water Hotline or by calling (800) 426-4791.