Cysts, in the context of water, refer to the protective, dormant stage of certain single-celled parasites. Their presence in water sources can pose health risks if ingested, making knowledge of their characteristics, contamination pathways, and effective removal methods essential for ensuring safe drinking water.
Understanding Waterborne Cysts
Cysts are the environmentally resistant, dormant form of certain single-celled parasites, specifically protozoa, that can survive outside a host in harsh conditions. Their protective shells allow them to endure various environmental stresses, including temperature fluctuations and common disinfectants. Once ingested by a suitable host, the cyst wall dissolves, releasing the active parasitic form that can then cause illness.
Two common types of waterborne cysts are Giardia intestinalis and Cryptosporidium parvum. Giardia cysts are typically oval-shaped, measuring about 11-14 micrometers. Cryptosporidium oocysts are generally smaller, around 2-4 micrometers. Both are invisible to the naked eye, highlighting the need for robust water treatment and prevention strategies.
How Cysts Contaminate Water
Waterborne cysts primarily enter water sources through fecal contamination from infected humans and animals. This can occur through various pathways, including agricultural runoff, which carries animal waste from livestock operations into rivers and lakes. Wildlife, such as beavers and muskrats, can also contribute to the presence of Giardia in surface waters.
Improperly treated sewage and wastewater discharges are significant sources of contamination. Sewage overflows or leaking septic tanks can introduce cysts into ground and surface water. Even in areas with seemingly high-quality water sources, cysts can be present, especially in surface waters like lakes, ponds, rivers, and streams.
Health Implications of Ingesting Cysts
Ingesting water contaminated with these cysts can lead to gastrointestinal illnesses. Giardia intestinalis causes giardiasis, while Cryptosporidium parvum leads to cryptosporidiosis. Symptoms for both can include watery diarrhea, abdominal cramps, nausea, vomiting, and fatigue. The onset of symptoms typically ranges from 1 to 3 weeks after exposure for giardiasis and 2 to 10 days for cryptosporidiosis.
While healthy individuals usually recover from these infections within a few weeks, symptoms can be more severe and prolonged for vulnerable populations. Young children, the elderly, and immunocompromised individuals are at higher risk for serious complications, including severe dehydration and malnutrition.
A significant challenge in water treatment is the resistance of these cysts to common disinfectants. Both Giardia and Cryptosporidium have a tough outer shell that provides considerable protection against chlorine, the most widely used water disinfectant. This inherent resistance means that chlorine alone may not be sufficient to inactivate them, necessitating additional or alternative treatment methods to ensure water safety.
Protecting Your Water from Cysts
To protect against waterborne cysts, several effective methods can be employed at the household level. Boiling water is a highly reliable method for inactivating both Giardia and Cryptosporidium cysts, with a rolling boil for at least one minute being sufficient. This heat effectively destroys the parasites, making the water safe for consumption.
Filtration is another widely used and effective treatment. Filters designed to remove cysts typically have a pore size of 1 micron or less. Filters certified by organizations such as NSF/ANSI standards 53 or 58 specifically for “cyst reduction” or “cyst removal” provide assurance of their efficacy against these parasites. Reverse osmosis systems are also effective in removing cysts.
Ultraviolet (UV) light treatment is an alternative disinfection method that can inactivate Giardia and Cryptosporidium. Beyond these treatment methods, general prevention practices are also important. This includes being aware of local water advisories, practicing good personal hygiene, especially after contact with animals or before handling food, and avoiding swallowing water in recreational settings like pools or lakes.