Water Purification

We never know the worth of water till the well is dry. - Thomas Fuller

Purification is something that can be easily accomplished, using a multitude of technologies that are available, ranging from boiling water, ceramic filters and ultraviolet light.

Most surface water contain some types of microorganisms (protozoa, bacteria, viruses) and/or pollutants (chemicals, foul odors, sewage, spilt fuel). Microorganisms are living microscopic cells that, when consumed, can cause diseases such as dysentery, cholera, typhoid and hepatitis.

Protozoa the largest of all microorganisms include such parasites as Giaridia Lamblia and cryptosporidium. Bacteria medium-size microorganisms include E. coli, Vibrio Cholerae, campylobacter, and salmonella, all of which are found in human and animal waste. Viruses are the smallest of all the microorganisms. They include hepatitis A and E, Norwalk virus, rotavirus, poliovirus and echovirus.



If the water is cloudy, the first thing to do is take out as much of the dirt as possible. If you have time, start by letting it settle. Put the water in a tall container and leave it for 12 to 24 hours. Carefully dip or pour the cleaner water at the top into another container. Clean the water as you put it in the new container by running it through a filter. The easiest filter is a coffee filter. If you don't have a coffee filter, use a paper towel, cheesecloth, a cotton plug in a funnel or a piece of clean t-shirt material or similar cloth. Change the filter whenever it gets visibly dirty.

Once water is filtered, it is fine for using to clean things like clothing and floors. Don't use water that you wouldn't drink to wash you face, rinse your dishes or clean kitchen utensils.

Once you have filtered the water, it has to be treated before it's safe to drink. The purpose of this is to kill all the germs that may be in the water. There are several ways to treat surface water for disease-causing microorganisms. Each method has its advantages and disadvantages. Realize that no method is perfect and sometimes combining methods is the best solution.

  • Heat (boiling and distilling)
  • Disinfectant (purification, chemical)
  • Filters
  • Light (ultraviolet).



Boiling water has been the main way to disinfect water from microorganisms because it kills them all if done correctly. Water should be brought to a rolling boil for at least five minutes and preferably up to 10 minutes. If you live at high altitudes, add a minute for every 1000 feet above sea level. Bacteria and protozoa are dead at the first bubbles.

There are drawbacks to boiling water:

Boiled water tends to taste flat because there is no air in it. You can add the air back by pouring the water back and forth between two clean containers. This will also improve the taste of stored or bottled water.

  • It does not eliminate many chemical pollutants, radiation or heavy metals.
  • Boiling can require a lot of fuel and cooking equipment
  • The long cool-down period
  • Some of the water will evaporate before it is ready to drink
  • The water will still have particulate substances in it (requires filtering)
  • It does not eliminate poor taste or foul odors
  • Difficult to treat very much water at a time

Solar Still

Solar stills operate upon the "greenhouse effect." A clear plastic barrier (a plastic bag, ground cloth, or a plastic grocery sack) is placed over a "source," such as the ground, tree branches or other organic materials. The sun's (solar) energy passes through the barrier and heats the source material. Moisture from the source vaporizes, rises and then condenses on the underside of the plastic barrier. The moisture is then collected as drinkable water. Solar stills are capable of distilling almost any tainted water, even seawater. Solar stills can condense drinkable water from substantially anything that contains moisture.

The only source materials that it cannot distill drinkable water from are materials that give off toxins, such as fluids with high amounts of chemicals, radiator fluids, and fuels.


Ceramic elements (most expensive, most durable, and maintainable) have the smallest pore size (0.1-0.5 microns). Ceramic elements can filter only free floating particulates and microorganisms. They do not remove chemicals, poor tastes, odors, or pollutants. Outside of boiling, commercial purification/filter devices made by companies such as PUR or Katadyn are the best choices. They range in size from small pump filters designed for mobility to large gravity filters designed for camps, no pumping is required. On the down side, most such filtering devices are expensive and have a limited capacity. Filters are good for anywhere from 200 liters to thousands of gallons, depending on the filter size and mechanism. Some filters used fiberglass and activated charcoal. Others use impregnated resin or even ceramic elements.

Glass fiber elements and compressed surgical paper (mildly expensive, medium durability, and usually not cleanable) also have small pores (0.2-1.0 microns). Like the ceramic filter, they remove only particulates and microorganisms, but they do not help much with pollutants. These are good low-cost filtering elements for home, backpacking and scouting needs, but they are not good for long-term storage because they can develop mold and mildew and they are hard to clean.

Hard-block carbon elements (less expensive, brittle, and not cleanable) have a small, but still effective pore size (0.4-2.0 microns). They are also used as an absorption filter. The best contribution that carbon makes to filtering is its ability to reduce chemical quantities, poor taste, odors and many pollutants. Because carbon is only mildly effective in filtering out particulates and microorganisms, it is mostly used as a second or third stage filter in home and portable water use. It is seldom used as a stand-alone filtering unit.


Two primary chemicals are used for purifying water: iodine and chlorine. These two chemicals are lightweight, low-cost and relatively easy to use.

Iodine has been found to be very effective against viruses, bacteria, and protozoa with the exception of cryptosporidium. Using iodine has some drawbacks.

  • Iodine is a short-term water-purification solution and should not be used regularly for more than three months.
  • The colder the water you wish to disinfect, the more required time is needed for disinfecting.
  • Because iodine is absorbed into dirt and debris, which is found in water, its purification dosage varies.
  • Pregnant women and people with thyroid conditions should not drink water purified with iodine.
  • Unpleasant taste of the water.

Chlorine bleach can also be used to purify water. The Federal Emergency Management Agency (FEMA) and the Red Cross have recommended using Chlorine Bleach to purify raw water. There are some drawbacks to the chlorination method.

  • Chlorine is very poisonous and adding too much can cause illness, internal organ damage or even death.
  • If the household bleach is over six months old, it may not have enough potency to disinfect.
  • You should only add it at the time you intend to use your water, NOT when you store it.

Because of the limited shelf life of chlorine bleach, Granular Calcium Hypo chlorite is an alternative you might want to consider.


Ultraviolet (UV) disinfection of water is a chemical-free process. UV radiation attacks the vital DNA of the bacteria directly. The bacteria lose their reproductive capability and are destroyed. Even parasites such as Cryptosporidia or Giardia, which are extremely resistant to chemical disinfectants, are efficiently reduced. The sterilized microorganisms are not removed from the water. UV disinfection does not remove dissolved organics, inorganic compounds or particles in the water.


  • Rapid treatment
  • More efficient than boiling


  • Suspended particles are a problem because microorganisms buried within particles are shielded from the UV light, a prefilter should be used.

Comparison Chart of Treatment Methods

Method/Device Neutralizes
Affects Taste Portable Notes
Boiling All No No Leaves flat taste. Yes Best method for killing
(1 micron)
Yes Some Improves Yes Effectiveness is based on pore
size and membrane technology.
Purifier All Yes Some Improves Yes Reduces all forms of
Chemicals Protozoa-Limited
No No Adds chemical tatste. Yes Slow to neutralize
Distillation All Yes Yes Improves, can make
taste flat.
No Very Slow
Ultraviolet Light All No No No Yes Does not work as well in
cloudy water.