RAFT bulk water filtration system for remote expeditions

Currently the easiest way to treat water suspected of carrying giardia is by purifying or filtering. But which device meets your needs? Let's look at the options.

U/V Purifiers

Ultraviolet light is known to kill both giardia and cryptosporidium, and several devices utilizing this technology are on the market. These devices work by exposing the water to an illuminated wand of light. One of the most common and effective is the "SteriPEN", which is available in several configurations (including models that use a solar panel to charge the batteries. To use the device, simply turn the light wand on, and use it to stir the water in your bottle for a minute or so. The amount of time needed for treatment depends on the volume of water. For 16 ounces, a minute is about right. For larger quantities a longer exposure is required. The device uses lithium-ion (Li-ion) batteries that last for several thousand treatments, depending on the size of the unit used, and the amount of time needed per treatment. Another device by the same company eliminates the batteries completely and relies on a hand crank to power the bulb instead.

Personal Water Filters

Several styles of small water filters are on the market, and your choice depends on your anticipated use, how much hassle you're willing to tolerate, and your personal preferences.

Drinking-Straw and In-line Filters

Several filtration systems utilize a filter element inserted in a straw or drinking tube, or a filter element secured inside the lid of a water bottle. While these are effective in removing most contaminants, including silt, they clog quickly and require constant cleaning in order to be effective.

Pump Filters

The best personal water filters on the market are the type that require pressure to work. Pressure is typically created by pumping a handle, which forces water through the filter element. Filter elements usually utilize a permeable ceramic element, and sometimes incorporate a charcoal element as additional protection. Ceramic filters eventually clog and they must be cleaned periodically to maintain efficiency. Cleaning is done in the field, and usually takes only a few minutes.

Placement of the pump handle is a consideration when selecting a filter. Devices that pump from the end, using a t-handle are hardest to use, and the user becomes tired after a while. A better ergonomic design uses a handle that pumps from the side. This design makes it easier to fill a couple of water bottles without the strain imparted by end-pumpers.

Another consideration is how water gets from the filter to your bottle. Most filters use a small hose that secures to the outflow end of the filter, with the end of the hose sitting inside the water bottle. Devices like this require the bottle to be placed on a flat, level surface that does not allow the possibility of the bottle being accidentally kicked over in the process of filling it. A better design allows the water bottle to be secured directly to the filter itself, eliminating the need for an outflow hose and removing the possibility of the bottle being knocked over while filing it.

Bulk Water Filters

For groups of three or more, a bulk filter system is recommended. These are capable of producing larger amounts of water with less effort than the smaller filter systems.

Pump Filters

The most popular large pump filter is made by Katadyn. It looks like a bicycle pump, and works much the same way. Simply insert your intake hose in the water supply (bucket or the pond or creek), and place the outflow hose in your water jug. It produces about a gallon a minute.

Gravity-Feed Filters

Several companies make gravity-feed filter systems. The ultimate in simplicity, all you do is fill a bag with raw water, hang it from a tree or elevated position, and insert the outflow hose into the filter canister. Place your water jug under the spigot and turn it on. Pressure is created by the elevation of the water above the filter element. R.A.F.T. makes a popular model that filters three gallons in about ten minutes. The advantage of this system is that it works while you're doing something else.

Maintaining Your Filter System

For filters to work effectively they must be maintained. Otherwise they will not allow good water flow, or they can become cracked and lose their effectiveness.


Filters become clogged in the field, and they need to be cleaned periodically in order to keep them flowing correctly. In most cases, this involves opening the housing and removing the ceramic element. Scrub the element with a scratch pad, rinse it off, and re-assemble. If you're filtering turbid water (water with lots of plant debris or silt), cleaning must be done frequently.

Protection from Freezing

Ceramic filters can freeze in low temperatures. This not only keeps water from flowing through the unit, it can also result in the ceramic element cracking. If a crack occurs and is not noticed, water will be contaminated and people will get sick from it. Keep your filter from freezing in the field in the following ways:

  • Place it in a cooler. The insulation in the cooler will keep it from freezing.
  • Place it near your sleeping bag. Wrap the filter canister in a plastic bag and place it partially under your sleeping bag to keep it warm.

Winter Considerations

Storing your filter over the winter requires attention to a few details. For starters, open the filter canister and remove the element. Let it dry for a few days. Store the unit with the cap off (to allow residual moisture to evaporate). If possible, store the filter in a heated area during the winter, if winter temperatures dip below freezing. This prevents the element from freezing and cracking. Finally, if the filter element develops mold or mildew, clean it with the scratch pad (no soap!), re-assemble it, and pump a bleach and water mixture through it to kill any residual mold or mildew. Following the bleach treatment, flush the element liberally with tap water, and pump clean water through it for several minutes to eliminate the bleach taste.