The style of water filter that you choose depends on your personal needs. Many people favor water bottles with the filter built in. Others choose a small hand filter that allows them to purify water as they pull it from the water source and dispense it into separate containers. If you have a water pack system that fits into your backpack, it's possible to purchase a water filter system that coordinates with it.
How you decide what water filtering system will work best for your needs depends on a variety of factors. If you travel with youngsters and plan on filtering their water, you'll probably want a separate hand filter. Many hikers like to add powdered drink mixes to their water. If you're one of these hikers, you probably don't want a water bottle filter. This way you can have separate drinking containers, one with your drink mix and the other with plain water. If you add drink mix to a water bottle filter, you won't be able to drink or filter any water until the bottle is empty.
If you're camping in wilderness in most parts of the world, a water filter that filters for bacteria, protozoa and parasites should be more than adequate. If you're headed for a Third World country or an area where the water may be exposed to sewage, your filter also needs to kill viruses.
Water filters that are equipped to kill viruses most often contain an iodine filtering system. Like iodine chemical tablets (which we'll learn more about later), this can adversely affect the flavor of your water. If you want the insurance of a filter that kills viruses, take along some ascorbic acid -- even the granulated orange flavored powders available at grocery stores will work. After filtering the water through the iodine system, add some of the powder. Ascorbic acid neutralizes the iodine, improving the taste. It also neutralizes the effectiveness of the iodine, so make sure that you follow the manufacturer's instructions for how long to let the water set in the iodine filter before adding anything else to the water.
Regardless of what type of water filter you choose, you don't want a situation where you are surrounded with water but have nothing to drink. A flow rate of one liter per minute is a good average to shoot for when shopping for a water filter.