Water Purification

There is a big difference between water filtration and water purification. Filters remove nearly all biological contaminants. Purifiers remove the very small biological contaminants such as viruses and some purifiers can remove the very small contaminants such as dissolved salts or toxins. For most applications a 0.1 micron filter is more than sufficient. In extremely fouled water a 0.02 filter is required. With extremely fouled water you will need an even finer level of purification to remove dissolved toxins such as lead.

Boiling Water

Boiling is an effective way to kill microorganisms and disinfect water. Boiling kills most bacteria immediately. It takes about three minutes of boiling to kill remaining microorganisms. Boiling has some disadvantages including:

  • Boiling does NOT remove debris, pollutants, chemicals, and dissolved materials such as salt and metals
  • Boiling takes time and fuel
  • Boiled water needs time to cool

Boiling kills microorganisms but does not remove other contaminants and debris. Boiling may help with some chemicals such as chlorine but it will do little to reduce dissolved solids such as metals, chemicals, and salt. In fact, water will boil away and make these other contaminants more concentrated. If you in a survival situation then your fuel may be at a premium and using large amounts of fuel to boil water may not be the best option.

When boiling water be sure clean or sterilize your cooking pot. Get a small amount of water to a rolling boil and swirl it around the inside of the pot. Be sure to clean the lip of the pot. Dump the water and then boil the water that you want to purify.


Using bleach is also an effective way to kill the very small microorganisms that filters could miss. You can use commercially available water purification tablets or a UV filter. If you do not have these then you can use household liquid chlorine bleach if it is pure, unscented, and contains 5% – 6% sodium hypochlorite. Use this table as a guide when purifying water using bleach.

Chlorine Concentration Drops/Quart Drops/Gallon Drops/Liter
1% 10/quart 40/gallon 10/liter
4-6% 2/quart 8/gallon 2/liter
7-10% 1/quart 4/gallon 1/liter

If you do not know the strength of the bleach then use 10 drops per quart/liter of water. If the water is cloudy, murky, or extremely cold then double this amount. You must mix or stir the water after adding the bleach and let it stand for at least 30 minutes before drinking.


A good water filter will remove debris, some chemicals, and most microorganisms from water. See the Getting Started page for filter recommendations. Use a good filter to pre-treat the water and then boil the water to kill the ultra-small microorganisms. If you have dissolved chemicals or metals in the water then a good filter may help but it will NOT remove all of those contaminants. Even a 0.02 micron filter will NOT remove these dissolved contaminants.