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Water Purification to Prevent Giardia

Topic Overview

The cold, clear water found in mountain streams and lakes may look appealing but often contains Giardia lamblia, the parasite that causes giardiasis. On short hikes, you may be able to carry from home enough water to drink. But when you are camping and backpacking, you often need to use other water sources. Water from pumps in campgrounds is usually safe, but if a sign tells you that the water is not safe or if you have any doubts, treat the water before you use it.

To avoid infection with Giardia lamblia and other parasites, use one of these purification methods:

  • Boil the water before using it for drinking, cooking, washing hands or dishes, or brushing your teeth. Bring the water to a rolling boil for 1 minute. If you are at an elevation of 6,562 ft (2,000 m) or higher, boil the water for 3 minutes. Even small amounts of water can contain parasites.
  • Add a chemical disinfectant to the water. Depending on the water temperature and how much sediment is present, you may need to let the water settle for several hours before you use it. You can find products to disinfect water in drugstores or camping supply stores. If the water is very cold or cloudy, increase the settling time before using it. Examples of chemical disinfectants are:
    • 5 tablets of halazone for 1 qt (1 L) of water. Treat for 30 minutes before using the water.
    • 1 Tbsp (15 mL) of crystalline iodine for 1 qt (1 L) of water. Treat for 30 minutes before using the water.
    • 0.1 tsp (0.5 mL) (about 5 drops from an eyedropper) of 2% tincture of iodine for 1 qt (1 L) of water. Treat for 70 minutes to 8 hours before using the water.
    • 2 to 4 drops (from an eyedropper) of household chlorine bleach for 1 qt (1 L) of water. Treat for 30 minutes before using the water. Iodine is considered to work better than chlorine against giardia.
  • Filter the water using a commercial filter specially designed for treating water. These filters range in price from $40 to $200 or more. The price generally depends on the quality of the filter and how fast it pumps water. Look for a filter that has these features, regardless of price:
    • Filter has an absolute pore size of 1 micrometer or less (will remove Giardia and some other parasites).
    • Labeling specifically states that it protects against Giardia.
  • Treat the water with a portable ultraviolet light that is designed to purify water. These devices can affect bacteria, viruses, and parasites so they can no longer reproduce. But these devices work best on water that has already been filtered and is clear.

Related Information

Credits

By Healthwise Staff
E. Gregory Thompson, MD - Internal Medicine
W. David Colby IV, MSc, MD, FRCPC - Infectious Disease
Last Revised August 8, 2013

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