Water Treatment
While on virtually any backcountry trek, safe drinking water is one of your most precious items. There are still a number of backpackers and canoeists that drink untreated water from lakes and streams. Unfortunately the incidence and severity of contaminated back country water makes this practice little better than just 'playing the odds'. The only way to avoid infection, or worse, from contaminated back country water is to treat all water intended for human use.
Water contamination results from siltation, decomposing organic materials, chemical sources, bacteria, viruses, and parasites. Removing chemical contamination is not practical with the equipment available to most outdoor groups. Chemical contamination can result when water leaches through rock outcroppings with high mineral concentrations or old mine tailings. Chemicals can also be introduced during flood conditions or by agricultural fertilizers and industrial processes. If the water looks brackish, smells foul, or if you are near old mines, farms or manufacturing centers, don't try to treat the water. Find another water source or plan on packing in what you need. Luckily, most water sources in the Sierras are free from chemical contamination, as long as you keep an eye out for old mines!
Except for chemical contamination, water can be purified adequately in the field by mechanical, physical and/or chemical means. All of the available field water treatment methods are attempting to lower the levels of harmful parasites, bacteria and viruses to the point where the body can defend itself. The resulting water won't be sterile, but it will be safe to drink for a healthy person.
In the field, the clearest water possible should be chosen or attempts made to clarify the water prior to starting any other treatment. Water that appears silty or cloudy often has a higher bacterial count and tends to be more heavily contaminated. As a minimum, cloudy or silty water should be allowed to stand in a covered container for several hours to settle out much of the debris. Clear water can then be ladled off the top for further treatment. Obviously, you'll need to plan ahead for this process. A bunch of thirsty Scouts aren't going to wait for the water to get clear!
One of the oldest and still most effective water treatments is heat. Bringing water to a boil will make it safe to drink at all safe hiking altitudes (at 25,000 feet water boils at 185degF). It is not necessary to boil for any specified length of time, just get it to a boil and you're good to go. In fact, at all elevations in the Sierras simply bringing the water to 175degF (hot drink temperature) will kill the pathogens that are found in the Sierras making the water safe to drink.
Chlorine water treatment has been in use by many municipal water systems for decades. Chlorine treatment is very effective against virus and bacteria in neutral to slightly acidic water. Some parasites, including Giardia, are resistant to chlorine. For this reason it is not recommended for use in the Sierras where Giardia can be found in virtually all water courses. But, if it's all you've got, it's better than no treatment at all! Organic debris (cloudy, sility water) reduces chlorine's effectiveness significantly. Adding 2 drops of laundry bleach (averaging 5% chlorine concentration) per quart of clear water can make most water safe to drink. Shake the water bottle after adding the bleach and let it stand for 30 minutes. The treated water should have a slight chlorine smell. If not, the bleach is not at 5% concentration and will not be effective. As Scout groups carry bleach for use in their dishwashing rinse water, chlorination is a practical backup plan.
Iodine water treatments are effective against viral, bacterial and many (but not all) parasitic contaminates. It is effective against Giardia. Some individuals are sensitive to iodine. Ask first! Iodine is more effective than chlorine in cloudy water, though clear water is still recommended. Tincture of iodine (2% iodine) from the first aid kit can be used for effective water treatment. Add 5 drops to each quart of clear water (10 drops to cloudy) and let stand for 30 minutes after shaking. The water will have a slight iodine taste to it but it will be safe. Iodine is available in tablet form as 'Portable Aqua' and several other commercial brands. These tablets are small and easy to pack, though, on a per gallon basis, they are expensive. They do make a good backup or emergency treatment. Follow the manufacturer's instructions, but there is always a waiting period of about 30 minutes for the tablets to be effective. All tablet forms of iodine have a shelf life. Be sure yours is still 'in date' before relying on it in the field!
BSA's High Adventure canoe base, Northern Tier, issues another iodine based product to all of its canoeing crews for water treatment.
Polar Pure uses iodine crystals held captive in a small calibrated jar. Water added to the jar becomes supersaturated with iodine. Capfuls of this supersaturated water are then added to your water for treatment. The jar also has a thermometer that indicates water temperature. The treatment time and quantity (capfuls) of supersaturated water are a function of water temperature. Treatment times should be doubled for cloudy or silty water. This crystalline form of iodine has no shelf life and is quite economical, though there is an iodine taste and the waiting time. Still, this method is one of the most highly reliable and effective techniques available.
Popular with lightweight backpackers and as a backup or emergency water treatment system, chlorine dioxine tablets weigh as little as 1 ounce for a multi-day supply (per person). Though a bit pricey at ~$2/gallon, this chemical treatment is very effective with a long shelf life. It's also simple use, drop 1 tablet in a quart of water and shake to start the treatment. Aside from the price, the main draw back is treatment time, up to 4 hours to treat for giardia in silty, cold (4 degC) water. Treatment times fall to 30 minutes with clear, warmer (20 degC) water. There is little to no after taste with this treatment.
Mechanical filters have become quite popular for water treatment due to their decreasing cost, good water taste, and minimal wait times. It is important to understand your filtering needs and the wide range of filtering capabilities if you choose to use a filter. The Center for Disease Control (http://www.cdc.gov/ncidod/dpd/parasites/cryptosporidiosis/factsht_crypto_prevent_water.htm) recommends that mechanical filters have an ABSOLUTE pore size (some ratings are average!) of no more than 1 micron to remove parasitic cysts, including Giardia. Further, as most bacteria have a diameter smaller than 1 micron and common viruses are as small as 0.2 microns, it is recommended that your mechanical filter have an ABSOLUTE pore size of no more than 0.2 microns. Water from filters with larger pore sizes should be chemically treated with chlorine or iodine or heated after filtering. Filters effective to 0.2 microns are prone to clogging if cloudy or silty water is used. The better models can be cleaned in the field, but it slows down the process. Using clear water is advised. Also, some manufacturers offer prefilters to remove silt and the like. Prefilters should be used to extend the cartridge life. Like all mechanical devices, filters can, and will, fail. Be prepared with a backup plan and/or a spare filter!
Good quality hand held filters can provide safe filtered water without chemical or heat treatment, though they are more expensive than other filters. One popular model with a rated capacity of 26 gallons retails for $40. Replacement cartridges sell for $30 making this filter as expensive to use as iodine tablets. Though convenient for individuals, the limited capacity of the hand held filters limits their use for Scout groups.
Pump style filters are commonly effective in the 0.2 micron range. Popular models are available starting at $54 with replacement cartridges starting at $35 for pumps rated for 200 gallons. Though more expensive than Polar Pure, these pump style filters provide safe water with a minimum of wait and no added taste. In fact, several models include activated charcoal filtering stages to help remove any objectionable tastes already in the water. For these reasons, these pump style filters are very popular with Scout groups. A word of caution: though popular, charcoal filter elements provide a bacteria friendly environment. It is advisable to pump chlorinated water through these filters before storing for your next trip. Some manufacturers even recommend freezing the filter cartridges to reduce bacteria.
Some new 'gadgets' on the market make water purification nearly fool proof, but they are expensive and are by no means 'Scout proof'. None the less, they bear mentioning for those with special needs. The SteriPen (http://www.hydro-photon.com/) purifies water using ultraviolet light. Its 4 AA batteries can treat up to 75 quarts of water with rechargeable NiMH batteries. At nearly $100 retail (plus batteries), it's expensive but, based on my first hand experience, very easy to use. MSR's MIOX purifier (http://www.msrcorp.com/filters/miox.asp) is slightly more expensive at $120 retail, uses fewer batteries, but takes longer to treat your quart of water ( 90 seconds for the Steripen vs 15 minutes for virus & bacteria & 30 minutes for giardia using the MIOX). Both are small, light weight and virtually fool proof.
The bottom line? For Scout outings go with a good quality pump style filter for quick water treatment. Carry iodine tablets or Polar Pure for a backup, or carry enough extra fuel to boil your water if your filter fails. Practice good field hygiene. Wash hands thoroughly with soap and water before preparing any foods, cooking, washing dishes, and of course, before eating.
Note: Filters collect germs from water, so anyone changing or cleaning the cartridges should also wash hands thoroughly afterwards!
This page revised March21, 2010