Boiling Water
Boiling water is an old and proven method. Boiling water is as simple as putting a pot full of water over a fire. As a general practice, water should be brought to a boil for 3 minutes and left to cool before drinking. This method will effectively kill protozoa, bacteria and viruses. Unfortunately, boiling will not remove contaminants such as chemicals or heavy metals. Boiling also requires more time and a fire source.
Chemical Treatment
There are a good variety of chemical treatments available. Like boiling, chemical treatments are only effective at eliminating organic pathogens. Chemical treatments usually come in a tablet which can be dropped into a water bottle. Each type of treatment will specify exactly how to treat the water and how long before you can drink. Some chemicals are also more effective than others. For example, iodine is popular but ineffective against cryptosporidium. Consult with manufacturer directions before using chemical treatments. Chemical treatments are also know to add a funny taste to the water. Chemical treatements are; however, very lightweight, making them popular amongst the ultralight crowd.
Filter
Water filters offer a great way to remove contaminants from water. Not only will filters remove bio-organisms, but can also remove chemicals and heavy metals. Most filters will also remove bad tastes from water. Filters use a pump or gravity to pass water through a membrane which removes contaminants. There are downsides to filters though. They are known to clog, can be damaged, they require physical effort, and can be relatively heavy. Also, most filters will be unable to remove the smallest contaminants, such as some viruses.
UV Treatment
This is one of the newest players in the water purification market. They are a small electronic device with a ultra violet light emitting bulb. The UV light does not kill organisms, but effectively renders them sterile. Like boiling and chemical treatment, this option will not remove inorganic contaminants. UV treatment is lightweight, quick and simple. Care must be taken when using UV treatment, because your batteries may run out or rough handling may break the bulb.