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
    • Labeling specifically states that it protects against
  • 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


ByHealthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine
Specialist Medical Reviewer W. David Colby IV, MSc, MD, FRCPC – Infectious Disease

Current as ofMarch 3, 2017