Water Safety

Amy Thomas Health Guide
  • All drinking water (even bottled water) contains microscopic parasites that can cause diarrhea, fever, and additional gastrointestinal complications. While most people can generally tolerate small amounts of these contaminants without getting sick, some may be more vulnerable to developing illness from drinking water-including people with cancer receiving chemotherapy, and especially those undergoing bone marrow transplantation. If you have a weak immune system related to cancer or cancer treatment, you should be aware of the small but real risk of drinking untreated tap water, and you should learn the fairly simple ways to protect yourself from water-borne illness

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    Microscopic parasites naturally find their way into our drinking water for a number of reasons, and suppliers often treat water with a disinfectant to kill these germs. But the disinfecting agents aren't universally effective, and their use is limited because they can react with other compounds in the water to form toxic byproducts. Water suppliers are challenged to balance protection from microbial pathogens while minimizing health risks to the population from disinfection byproducts, and as a result most drinking water contains a small amount of microbial organisms generally well tolerated by a healthy person.


    Cryptosporidium is a microscopic parasite with a thick outer shell that is particularly resistant to traditional disinfectants like chlorine and iodine. Though most people won't get sick from drinking a small amount of Cryptosporidium-contaminated water, this microbe can cause diarrheal disease that is serious, long-lasting, and potentially fatal in people with weak immune systems. While the risk of contracting Cryptosporidial disease from tap water is not well defined enough to recommend all immuno-suppressed people avoid or treat their own tap water, some individuals may prefer taking extra measures to avoid waterborne illness.


    Boiling water for one full minute is the most effective way to kill the microparasite, but alternative ways include a getting point of use filter that uses reverse osmosis and removes particles one micrometer or smaller, or drinking bottled water. If you're considering a point-of-use filter, look for one labeled as "Absolute" one micrometer filter, or those labeled as certified by NSF International (National Sanitation Foundation) for "Cyst Removal." Filters with the "Nominal" one micrometer rating may not reliably remove Cryptosporidium. And all bottled waters aren't equal. Variables include the source water origin and the treatment of the water prior to bottling. Bottled waters from protected wells and protected spring water are typically the safest. Bottled waters treated with distillation or reverse osmosis, and commercially filtered bottled waters are also usually free of Cryptosporidium.


    If your immune system is weak from cancer treatment, you should talk to your physician about which precautions you should take to avoid water-borne illness. Recommendations may vary, depending on the cause and degree of immunosuppression. To learn more about your local drinking water and water programs authorized under the Safe Drinking Water Act you can call The Safe Drinking Water Hotline, (1-800-426-4791). The Hotline addresses questions about local drinking water quality, drinking water standards, protection of source water, septic systems, and wells. Some additional precautions for everyone include the following:


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    • Take care not to swallow recreational water (swimming pool water)
    • Do not drink untreated water from shallow wells, lakes, rivers, springs, ponds, and streams.
    • Avoid untreated tap water during outbreaks of disease caused by contaminated drinking water.
    • Avoid tap water that has not been boiled (including ice not been made from boiled water!) when the public health department issues a boiled water advisory
    • Avoid untreated ice or drinking water (even for brushing your teeth) when traveling in countries where the water supply might be unsafe.
Published On: December 11, 2008

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