Boil Water Advisories: Managing Cryptosporidium Risk in Buildings

Boil Water Advisories: Managing Cryptosporidium Risk in Buildings

By Hilary Nardone, Senior Permitting Manager 
Certified ASSE 12080  Legionella  Water Safety and Management Specialist  

Municipal Water Utilities or local health officials may issue boil water advisories when parasites such as Cryptosporidium are identified in the community’s drinking water.  Cryptosporidium is most commonly spread through drinking water and recreational water and can cause gastrointestinal issues including diarrhea.  They may pose a greater health risk for infants, young children, the elderly, and people with compromised immune systems. 

While in municipal drinking water supplies, chlorination and chloramination are used to safely disinfect drinking water by killing most viruses and bacteria, studies have shown that Cryptosporidium can be more resistant to these disinfectants.  Therefore, the CDC recommends the following actions for drinking water that may be contaminated: 

  • Use commercially bottled water. 
  • Use water that has been boiled for 1 minute and left to cool.  At elevations above 6,500 feet (1,981 meters), boil water for 3 minutes. 
  • Use a filter designed to remove Cryptosporidium
    • The label might read “NSF 53” or “NSF 58.” 
    • Filter labels that read “absolute pore size of 1 micron or smaller” are also effective at removing Cryptosporidium. 
Image Source: CDC/ Jonathan W.M. Gold, M.D.

During a boil water advisory, it is expected that less water will be consumed than during times of normal operation.  This could lead to stagnation in water distribution piping which, in conjunction with loss of disinfectant and disruption of biofilm, may make building water systems more susceptible to the growth and amplification of other waterborne pathogens including Legionella bacteria, E. coli and coliforms.

In addition to following your facility’s Emergency Water Supply Plan, taking small practical steps at your facility can help minimize the risk of bacteria contamination in your drinking water systems. Per CDC, the following are some control measures to take at your facility when a boil water advisory is lifted: 

  • Flush, clean and sanitize equipment with water line connections per manufacturer’s instructions. 
  • Flush pipes, faucets and drinking water fountains for at least 5 minutes. 
  • Drain and refill hot water heaters set below 113°F. 
  • Change all point-of-entry and point-of-use water filters, including those associated with equipment that uses water.

Additional resources on Boil Water Advisories can be found in the following pages:  

Boil Water Advisory | Water, Sanitation, & Hygiene-related Emergencies & and Outbreaks | Healthy Water | CDC 

General Information | Cryptosporidium | Parasites | CDC 

Hospitals, Healthcare Facilities, & Nursing Homes | Cryptosporidium | Boil Water Advisories | CDC 
Boil Water Notices – Frequently Asked Questions for Hospitals and Other Resident Medical Facilities ( 

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