Water by its very nature is always pure, since the bond between its hydrogen and oxygen atoms is extremely strong. The problem is that almost all of the world's water supply must share space with organic material, chemicals, minerals and manmade pollutants. The result is often an undrinkable solution, possibly containing deadly bacteria, viruses and other disease-causing agents. Fortunately, mankind has developed a number of water treatment methods which make our water supply much safer for consumption. Not all of these methods work on a large scale, but they all render untreated water drinkable to humans.
Perhaps the most basic form of water treatment is called settling. Untreated water gathered from a natural source can be left undisturbed in a container, allowing solids to settle out of the solution and fall to the bottom. After enough time has elapsed, the uppermost level of water can be drawn out for consumption.
This method has several major drawbacks, however. The settling process can take several days or weeks to be effective, and there is no protection against bacteria or other organic materials which may not settle out. If the water source is relatively clean, such as a mountain stream in remote territory, the settling method may be adequate.
A more thorough and faster form of water treatment is the boiling method. Water should first be filtered through a cloth to remove larger contaminants, then placed in a clean metal container. Virtually every bacteria or other hazardous lifeform will not survive the boiling process, although experts suggest maintaining a rolling boil for several minutes to ensure success.
Once the water has cooled, it should be safer to drink. One drawback to the boiling water treatment method is the possibility that inorganic solids may still remain. Boiling large amounts of water can also be very time-consuming.
One form of water treatment which works on a large scale is chemical disinfection. Questionable water can be rendered drinkable, if not particularly flavorful, by the addition of iodine or chlorine-based tablets. Chemical agents destroy many of the bacteria and other organic contaminants found in natural water supplies. The pills carried by hikers and campers usually contain a form of iodine, although some people with iodine allergies may use chlorine-based tablets. Chemical water treatment is also the preferred method of swimming pool operators, since the chlorine kills a number of contaminants brought in through fecal matter.
For homeowners concerned about their public water supplies, another form of treating water has become increasingly popular. Filtration through activated charcoal or paper filters is a low-cost method used in many private homes. Tap water flows through a small filter at the end of a faucet or through a more elaborate system in the basement or kitchen.
The principle behind the filtration method is that heavy metals, organic contaminants and many bacteria are simply too large to pass through the mesh of a filter. The water molecules which do pass through are much more pure, providing a better tasting product. Filters must be changed regularly to be effective, however. Bacteria can grow on filters clogged with organic material.
For those who may want an even more discriminating method, there is reverse osmosis. Many water treatment companies and bottled water producers use reverse osmosis along with other methods such as filtration or ozonation. Reverse osmosis requires the use of a semi-permeable material with extremely small openings. Untreated water is forced through this membrane, which prevents even the smallest forms of bacteria and chemical pollutants from passing. The water molecules themselves actually change in order to pass through the membrane. The resulting water supply is said to be 'wetter', because the individual water molecules have fewer sides and are more easily absorbed by the body.
Other forms of water treatment may included ozonation, ionization and ultraviolet light exposure. Ultraviolet light treatment will destroy the DNA of any harmful bacteria present in the water, but the cost of installing and operating such a treatment system in a home can be prohibitive.