Two Ways to Purify Water

Hiker filling her water bottle at the Grand Canyon North Kaibab Trailhead water bottle filling station
Hiker filling her water bottle at the Grand Canyon National Park North Kaibab Trailhead Water Bottle Station.


Are you going to explore the great outdoors? Before you head out on your trip, find out if there are potable drinking water sources in the park and locations where water is available along your adventure. Bring enough water for you and your group to last your whole trip. If potable water is not available, learn how to purify and disinfect natural water before you head out. Drinking from unpurified water sources can result in waterborne diseases, such as cryptosporidiosis or giardiasis. Never drink water that you haven’t treated from a natural source, even if the water looks clean.

“Potable water” is clean water that’s safe to drink, brush your teeth with, wash your hands with, and use for preparing food. Information on water sources can be found on the official NPS websites of most parks. If you can’t find the information you need online, use the park contact information to ask about water quality and if water treatment is needed at your destination.

If you’re active outdoors (hiking, biking, running, swimming, etc.), especially in hot weather, you should plan to drink about one-half liter to a full liter per hour to remain hydrated. One liter is about the same as four cups, or two 16.9-ounce water bottles. Prepare your water before you need it and drink before you get thirsty. Do not allow yourself to become dehydrated. Symptoms of dehydration range from mild to severe. Mild to moderate symptoms include thirst, dry mouth, headache, dizziness, and decreased urine output. More severe symptoms can lead to worsening dizziness, severely decreased urine output, a loss in blood pressure, rapid heart rate, shock, seizure, coma, and can be fatal. Seek immediate medical attention if you are experiencing worsening or severe symptoms of dehydration.
Visitor filtering water at Cosley Lake in Glacier National Park
Visitor filtering water for drinking at Cosley Lake in Glacier National Park


Here are some steps on how to purify water from a natural source if potable water is not available:

  • Start with a clean container that has been disinfected. Wash your hands with soap and water before collecting water so you don't contaminate it.
  • Collect water from higher elevations or near the water's source.
  • Avoid taking water from where you see animals grazing or near established campsites.
  • Collect water from areas of moving water in rivers and streams, or the top few inches of a lake. Dip your bottle just under the surface and fill from there. Stagnant (standing or non-moving) water is a breeding ground for insects, bacteria and viruses and should be avoided.
  • Now purify your water for drinking. There are two ways to treat water for drinking:
  • Boiling
  • Filtration and Disinfection

How to purify natural, non-potable water

  • Boiling is the best way to treat non-potable water.
  • If you’re at an elevation below 6,500 feet, put the water in a container over a heat source, such as a campfire or propane stove, and bring to a rolling boil for 1 minute.
  • If you’re at an elevation over 6,500 feet, bring the water to a rolling boil for 3 minutes.

  • Most water filters are made of a screen with many tiny holes in it. These filters can remove protozoa and some bacteria, but viruses cannot be filtered out because they’re even smaller than protozoa and bacteria.
  • Filters also remove bigger contaminants like leaves, silt, dirt, and sand. If the water is cloudy or has floating material in it, you should filter it even if you plan to boil or disinfect it.
  • Filtration systems with absolute pore size less than or equal to 1 micron filter (NSF Standards 53 or 58 rated “cyst reduction / removal) have a high effectiveness in removing cryptosporidium and giardia.
  • Be sure to use and care for your filter according to the manufacturer’s instructions. Filters don’t work as well if they aren’t taken care of over time.
  • Filtration must be followed by disinfection to purify water for drinking.

  • Disinfection happens when a chemical kills bacteria, viruses, and other potentially harmful organisms in your water.
  • Chemical tablets or liquid drops are the most common ways to disinfect non-potable water. National Sanitation Foundation (NSF) approved products are recommended. - Iodine or chlorine dioxide are the most frequently used disinfection agents.
  • Follow the manufacturer’s instruction for disinfecting the water. Treatment time to disinfect the water for drinking varies by product. If the water is cloudy or has floating debris, it will be more effective to pre-filter the water before disinfecting.
  • WARNING: Do not use pool-cleaning tablets to disinfect drinking water! Pool-cleaning tablets are not intended to be consumed.
  • WARNING: Consult with your physician before using any drinking water disinfection products. Some tablets or drops, especially iodine, may not be safe for pregnant women, people with thyroid issues or iodine hypersensitivities, or for long periods of time.

Learn more about Backcountry Water Treatment (boiling, filtration and disinfection) and waterborne illnesses and symptoms from the Centers for Disease Control and Prevention (CDC).

Learn more about exercising outdoors in heat.

Learn more about the warning signs and symptoms of heat related illness.

Last updated: November 29, 2017