In the second part of the series on backcountry water treatment, we dive into chemical disinfection methods. This article builds on concepts introduced previously, focusing on the three major classes of chemical disinfectants, their pros and cons, effectiveness, and practical strategies for use in the field.
Introduction to Chemical Disinfection
Chemical disinfection is a crucial method for ensuring safe drinking water in the backcountry. It involves using chemicals to kill pathogens in water, making it safe to drink. The three major classes of chemical disinfectants for backcountry use are iodine, chlorine, and chlorine dioxide. Each has unique strengths, limitations, and potential side effects.
Iodine
Iodine is one of the oldest and most well-known chemical disinfectants. Developed for the US Army in the 1940s, iodine tablets have been used by outdoor enthusiasts for decades. Each tablet contains 8 milligrams of iodine, and it takes two tablets to treat one liter of water. However, iodine leaves a brown tint and a distinct taste in the water. To counteract this, ascorbic acid (vitamin C) tablets can be used after the treatment time to neutralize the taste and color, but this also deactivates the disinfection properties.
Potable Aqua Iodine Tablet Kit (Amazon, $10)
Drawbacks of Iodine
- Health Risks: The maximum recommended dietary dose of iodine is 2 milligrams per day, but in emergency situations, higher doses may be necessary. Some individuals, particularly those with subclinical hyperthyroidism, may experience adverse effects such as rashes, gastrointestinal upset, and thyroid issues.
- Effectiveness: Iodine is less effective against certain cysts, particularly Cryptosporidium. Studies show that iodine takes longer to inactivate Giardia and is almost ineffective against Cryptosporidium even after extended exposure times.
Chlorine
Chlorine is the most widely used disinfectant in municipal water systems. It is effective against bacteria and viruses at lower concentrations compared to iodine. Liquid bleach (sodium hypochlorite) is a common household source of chlorine for water disinfection. The recommended dose is two drops per quart of water, increasing to three drops if the water is cloudy.
Drawbacks of Chlorine
- Effectiveness Against Cysts: Like iodine, chlorine is not effective against Cryptosporidium at practical concentrations. Chlorine-resistant pathogens require higher doses and longer contact times, which may not be feasible in the field.
- Byproducts: Chlorine can react with organic matter in water to produce potentially carcinogenic byproducts such as trihalomethanes and haloacetic acids.
Chlorine Tablets (Amazon, $30)
Aquatabs Chlorine Tablets (Amazon, $15) Sometimes these are cheaper than the bottle!
Chlorine Dioxide
Chlorine dioxide is a neutral chlorine compound that disinfects by oxidation. Unlike chlorine, it does not produce free chlorine in water, reducing the risk of harmful byproducts. Chlorine dioxide is effective against all types of pathogens, including Cryptosporidium, Giardia, bacteria, and viruses.
Advantages of Chlorine Dioxide
- Effectiveness: It is more effective than chlorine and iodine, especially at higher pH levels. Chlorine dioxide can inactivate Cryptosporidium at practical doses and contact times, making it a superior choice for comprehensive water disinfection.
- Reduced Byproducts: Chlorine dioxide produces fewer harmful byproducts compared to chlorine.
Potable Aqua Chlorine Dioxide Tablets (Amazon, $16)
Katadyn Micropur MP1 Tablets (Amazon, $14)
Practical Considerations
Chlorine dioxide tablets typically require a longer treatment time (up to four hours) to ensure the inactivation of Cryptosporidium. However, for bacteria and viruses, the treatment time can be much shorter, around 15-30 minutes. This makes chlorine dioxide a versatile and effective option for backcountry water treatment.
Practical Scenarios and Recommendations
- General Use: For most backcountry situations where viruses are not a primary concern, using a filter in combination with chemical disinfectants can provide comprehensive protection. Filters can remove larger pathogens like cysts, while chemicals can inactivate bacteria and viruses.
- Primary Chemical Treatment: If using chemicals as the primary treatment method, ensure that the chosen disinfectant is capable of treating all pathogen types. Chlorine dioxide is the only option that meets this criterion, providing effective protection against bacteria, viruses, and cysts.
- Ultralight and Short Trips: For ultralight backpackers and short trips, chlorine dioxide tablets offer the best balance of weight, effectiveness, and convenience. They are lightweight, easy to use, and provide full pathogen coverage.
Conclusion
Chemical disinfection is an essential method for treating backcountry water. Each disinfectant—iodine, chlorine, and chlorine dioxide—has its own advantages and limitations. Understanding these can help you choose the most appropriate method for your needs. For comprehensive protection, especially against Cryptosporidium, chlorine dioxide is the preferred choice. Always consider the specific requirements of your trip, including water conditions and potential pathogens, to ensure safe and effective water treatment.
Stay tuned for the next installment in this series, which will focus on filtration options for backcountry water treatment.