Purification

Water purification is serious business. Water impurities can make you very sick for weeks. Even remote streams can carry contaminants from animal feces that are dangerous to ingest. I carry a simple hand-pumped filter plus iodine tablets as a backup. A backup is required because pumps need periodic cleaning in the field and it's easy to lose a part (believe me). I put a coffee filter over the end of the infeed tube of my pump. The coffee filter, held in place with a rubber band, dramatically reduces the number of times you have to clean out the pump.

Don't try to drink seawater. Filter seawater only with a sea water specific filter system (see below).

[edit] Purification Options

Fresh Water Purifiers

There are many brands and types available now. Some only filter out bacteria, others filter out or treat viruses as well. Do your homework on this. Brita filters are not suitable for outdoor filtration.

Salt Water Purifiers

These are expensive and difficult to use. They rely on reverse osmosis (RO) filtration to reduce the salinity and purify the water. Reverse osmosis requires a lot of pressure and that pressure is generated by your arms. While fresh water purifiers can deliver several liters an hour, portable RO purifiers barely produce enough for one person before they are tired.

Iodine Tablets

Cheap and readily available. These are useful but have their limitations. The purity of the water is dependent on the time of exposure to the iodine and that is a function of water temperature, suspended solids and so on. Shelf life is limited and the tablets turn into lots of pink fibers over time.

Chlorination with Bleach

An old technique generally frowned on today. You can use commercially available liquid laundry bleaches; they are basically heavily chlorinated water. However, the time and amount to use is variable and the results can be iffy.

Chlorine Dioxide Drops

One of the newer products on the market. These are two-part formulas. The two parts are mixed into the water when you need purification.

Chlorine Dioxide Tablets

Another one of the newer products on the market. The advantages of chlorine dioxide drops with the convenience of tablets.

Boiling Water

Bringing fresh water to a boil will usually make it safe to drink. Boiling for five minutes usually makes it sterile. There are some exotic critters out there that can survive five minutes of boiling, but unless you paddle around undersea volcanic vents, you probably won't encounter them. Boiling water does consume fuel, which is not a good thing. Boiled water tastes flat - if you don't like this, make sure there's some air in the water container and shake it vigourously to aerate the water.