How to Purify Water

“Water, water everywhere and not a drop to drink.” as the old saying goes. A more apt statement for these times might be, “water, water everywhere, but is it safe to drink?” And if it’s not, what is a reliable water purification process?

Sadly, in this day and age there are few, if any, places where the water is safe to drink without treating, no matter how pristine and inviting it may look.

Water in the wild often contains harmful microorganisms, bacteria, and parasites that can cause a variety of ailments, such as giardia, dysentery, hepatitis, and hookworms. Luckily, however, we’re going to learn a few simple ways how to purify water to make it safe for consumption.


The simplest method to purify water is probably boiling.

You need to bring the water to a full, rolling boil for at least five minutes to be safe, with some experts recommending an even longer time. The downside to boiling your drinking water is that it removes the oxygen and the water ends up tasting flat. You can improve its quality by pouring it back and forth between two containers to put oxygen back in, or simply shake it up.


There are also several chemical purifiers on the market. Iodine comes in either liquid form (which can be messy), or tablet form.

One to two tablets or drops will clear up a quart of water. Shake your water bottle or container and wait twenty minutes before drinking. Water treated with iodine will have a darker color and a bit of an unpleasant flavor.

It is possible to mask this flavor by adding a powdered drink mix, but be sure to wait the twenty minutes before adding it, as it will interfere with the iodine’s effectiveness.

Other chemical treatments to purify water that work similarly to iodine are chlorine tablets, potassium permanganate, or halazone tablets. You should be able to pick these up fairly cheaply at most outdoor stores.

You can even add a few drops of bleach in a pinch, though I wouldn’t recommend overusing this one. It is important when using chemical purification to make sure all surfaces have been decontaminated.

After waiting the twenty minutes, slightly unscrew the lid of your water bottle or container and rinse around the threads and lid. The nice thing about using tablets is the container is very small and portable and can be slipped into a pocket, a plus if you do not want to carry a stove or pot, or take the time to boil water. Chemical treatment can be done on the hoof with minimal stopping time.


A third method of treatment is commercial filters. These come in all shapes, sizes, and price ranges. Most work by pushing the water through a charcoal or ceramic filter and then chemically treating it. Normally, they have one hose with a float that goes from the water source to the filter and a second hose, for clean water, that goes from filter to water bottle. When using this type of filter it is important to not cross-contaminate the hoses. Keep the clean hose in a separate plastic bag so it never touches the contaminated hose. The plus side to this method of how to purify water is that there is no flat or funky flavor. Commercial filters are also good for when the water is on the murky or dirty side, as they will remove this also. The drawback is that the sediment or tannins that you are filtering out will quickly clog up the filter. Some can be cleaned, with others you need to buy a replacement filter. Like all technical equipment, cost and breakage are things to be considered.

Primitive Methods

Beyond these common methods, there are more primitive techniques for the serious survivalists (or the unlucky person who was caught unprepared).

One is primitive filtering through soil or, preferably, sand. Keep rinsing the water repeatedly through the sand until it is looking clear. A variation of this is to dig a hole near where the source is and use the water that filters through into the hole. Be aware, that although soil is a good filter for sediment and other particles, it is not a guarantee for things like bacteria. This is even true for spring water, which many people assume is safe to drink without treatment. Click here for our article about making a survival water filter.

Distilling is a method that can be used for either collecting water or gathering freshwater out of saltwater. To collect water from the ground, dig a deep hole, and place a collecting container or water bottle in the center. Cover the hole with a clear sheet of plastic. The plastic needs to be weighted in the center with a rock or heavy object so that it points down into the container.

Then, secure the sides of the plastic tightly around the hole, such as by covering with dirt. The clear plastic acts like a greenhouse. The water in the soil evaporates as it heats up. When it hits the plastic it runs down to the point and drips off into the container. If all you have is saltwater, you can distill it by placing a small pot inside a larger pot. The salty water goes in the larger pot but not the smaller one.

Invert a lid over the pots that will point down into the smaller pot, then bring the water to a boil. As the water boils, freshwater will evaporate, hit the lid and drip down into the smaller pot, leaving the salt, or other minerals behind.

An alternative if you don’t have a smaller pot is to put a cloth over the pot the will absorb the steam. Use caution when removing it to wring it out so you don’t get burned.

Be Cautious

Above all, be cautious and use common sense when choosing where to gather your water.

Do the plants surrounding it look healthy?

Are there dead animals nearby that might have contaminated it?

Don’t collect any water that looks stagnant. Generally, water that is further upstream will be cleaner than that downstream, but there are no guarantees.

Don’t automatically go for the fasting rushing water, as fast water carries more sediment. You can avoid picking up a lot of sediment by making sure you dunk your water bottle completely under the water. This will avoid all the dirt and debris that floats on the surface.

With so many ways to purify water, there should be something for everyone and no reason to ever take chances drinking untreated water.

There are die-hards out there who will argue that the risk is small and not worth worrying about. But a nasty case of beaver fever in the backcountry can be not only uncomfortable, but life-threatening.

Diarrhea and vomiting can cause serious dehydration and sap your strength to the point that you can get yourself to safety.

If you are going to spend time in the outdoors, always make sure you have at least one, if not two or more, methods for purifying water. It’s vital to know water purification process methods. Make sure you view our Giardia article to be aware of the hazards of water that has not been purified.
Cathy Ellis is a teacher at Adirondack Wilderness Challenge, a wilderness adventure program for court adjudicated youth.
Wilderness Awareness School