Keep yourself safe and hydrated with the best equipment and techniques.
Heating. The surest method of making your water safe is to bring it to a boil, then let it cool. At higher elevations, boil it for several minutes to kill microorganisms because the boiling temperature of water will be lower.
Chemical. Available at most camping supply outlets, water purification tablets will kill most waterborne bacteria. The tablets contain iodine, halazone or chlorine. Over time, an opened container will lose its potency. Probably best to replace opened bottles after six months. For clear water, drop one tablet (8mg) into a quart or liter of water and let it stand 10 minutes. Add 10 minutes if the water is cold or discolored; 20 if both.
Filter. Most entry level, inexpensive filters will filter between 1.0 to 4.0 microns-they generally are targeted to eliminate giardia and sediment. Giardia is approximately 2.0 microns in size. So get a filter that will filter below that. Examples: Timberline and Coughlan. Use in wilderness camping. These basic filters have been used successfully in the Colorado River, Uinta and Windriver Mountains. Cost: about $18-29. They will last about two or three summers of active camping, or about 100 to 400 gallons, depending on the purity of the water you are filtering. Extend the life of any filter by keeping the filter screen away from sediment or the water source bottom
Microfilter. Microfilters are generally more expensive, but eliminate more than just the larger microorganisms. Some claim to remove 99.9% of all bacteria, as well as cysts, protozoa and tape worms. No filter is effective against viruses, such as hepatitis. Viruses are unlikely to be encountered in wilderness camping or from natural water sources. Microfilters generally filter between .02 to 1.0 microns and eliminate giardia and most bacteria. Examples: SweetWater Guardian, PUR Hiker. Use for outdoor camping from natural water sources. If a charcoal filter is present, it may also remove chemicals. Some of these can be field cleaned to extend the life of the filter. Cost: about $49-80.
Purifier. Filters to .004 microns and has a silver nitrate or iodine matrix-eliminates giardia, bacteria and viruses. If combined with a charcoal filter, will eliminate iodine taste and other chemicals. Example: PUR Explorer. Cost: $80-$170.
In evaluating any filter or purifier, look to where you will be using it, the cost, water output, and ease of pumping. Those mentioned above pump about one quart per minute, which is adequate. Some are easy, like the SweetWater Guardian, which requires only two pounds of pump pressure. You can also add a virus/iodine "filter" to it for about $25.