This is Part 2 of a two-part series on water disinfection. Read Part 1, Drinking Water 101: What’s in the Water?
In the last post, we looked at the basics of water disinfection. This week, we’ll explore the key features of some water disinfection products for travellers and backcountry explorers.
Factors to consider
The water disinfection method you choose depends on the water quality at your destination, your budget, the size and weight of the product, how many people will be using it, its availability, and access to fuel or electricity.
Water disinfection products for travellers*
Filters come in a variety of sizes and can be appropriate for many types of travel. They range from small hand pumps, water bottles, and gravity bags for individuals to plastic and stainless steel buckets for small and large groups. Generally, filters are easy to use, but they can be heavy, bulky, fragile, and expensive.
Regular maintenance is important to keep filters working well, but filter cartridges will eventually clog and need to be replaced. When changing filter cartridges, wear gloves and wash your hands afterward. Always follow the manufacturer’s instructions for optimum performance and safety.
Note that most filters do not effectively remove viruses because viruses are small enough to pass through filter pores, so a second step is needed to make the water safe to drink. In this case, filters that combine multiple steps are useful: they filter out particles, cysts, and bacteria and then water passes through a halogen (like iodine resin) to kill viruses. Be aware that treating water with chlorine before filtration may damage some filters.
Hand pumps and gravity bags are good options for hikers because they’re compact and produce clean water quickly. Using a hand pump typically involves placing a hose in the water source and pumping water through the filter into a clean container. In a gravity bag system, one bag is filled with water and hung several feet off the ground. Water flows through the filter into another bag on the ground.
Water bottle filters are increasingly popular with travellers because of their convenience. Check your filter to make sure it’s effective at removing viruses, an important feature in populated areas due to fecal contamination. Some manufacturers now produce water bottle filters that also use halogens to remove harmful microorganisms.
Check this table on recommended filter pore sizes needed to get safe drinking water.
Granular activated charcoal (GAC) is a component in some filters. GAC binds chemicals to its surface and removes both tastes (such as chlorine) and toxic contaminants (such as pesticides). If there is a risk that the water is chemically contaminated, try to find a better water source and include GAC in your disinfection process. Note that there’s a limit to how much GAC can absorb: high concentrations of chemicals may not be completely removed by GAC filtration, so it’s always best to look for a less contaminated water source.
Chemical disinfection is the most common water disinfection method in the world. Chemical disinfection using chlorine, iodine, or chlorine dioxide is a can be a good choice for many types of travel, including travel to remote areas and short-term outdoor excursions. Halogens (iodine and chlorine) are cheap and portable but leave a chemical taste in the water. This can be remedied by adding fruit juice drink mix or a small amount of ascorbic acid just before drinking. Note that using halogens alone does not remove Cryptosporidium cysts and should be used in short-term emergency situations only.
Chemical disinfection requires an understanding of how to adjust the dosage and wait time to match the amount of water, water temperature, and clarity. The CDC is a good source for information on using chlorine, iodine, and chlorine dioxide.
UV products with a built-in timer are convenient for treating small amounts of clear water. UV products for travellers are small and light but require a supply of extra batteries. This may be a good option for travellers spending most of their time in urban areas where more batteries can be purchased. It’s not a great option for anything but short-term use in rural or remote areas as batteries may not be available and can be heavy to pack.
Tap water and clear surface water
Tap water in developing countries may need to be disinfected due to aging water treatment systems or inconsistencies in municipal water treatment. When treating tap water in a developing country or clear surface water in remote backcountry areas, any of these methods can be used alone: heating water to a boil, chlorine dioxide, or ultraviolet (UV) light. Tap water can also be treated with halogens.
If you’re treating clear surface water in areas near human and animal activity, any method can be used alone with the exception of filters, clarification, and halogens. In this case, use filters or clarification methods followed by halogens, heat, or UV.
Remember, heating water to a boil is the easiest and most reliable one-step method.
Treating cloudy water
You may have to use several steps when water isn’t clear. Use a clarification method like coagulation-flocculation, then treat water with heat, filtration, UV, or halogens. Tablets that combine flocculation and chlorine are also available.
Water disinfection in special situations
Other disinfection methods are less commonly used by travellers. Bucket-style ceramic filters are a good choice for expatriates and long-term travellers spending an extended period in one location. Ceramic filters remove most viruses but water should still be treated with heat, halogens, or UV.
Travellers on ocean voyages require reverse osmosis filters to desalinate water and remove harmful microorganisms.
In refugee camps and disaster areas with a hot climate and full sunshine, the solar disinfection (SODIS) method can be used. Water is stored in clear bottles on a dark surface for at least four hours, allowing UV rays and heat from the sun to inactivate harmful microbes and pasteurize the water.
* Field Water Disinfection by Howard D. Backer, Wilderness Medical Society, 2009.
IAMAT has no affiliation with the products listed above. Links are included to illustrate the variety of water disinfection products available.
By Daphne Hendsbee and Tullia Marcolongo.
Photo courtesy of Karl-Erik Bennion, freeimages.
A comprehensive guide, Field Water Disinfection, can be purchased from the Wilderness Medical Society.
The CDC Yellow Book provides a detailed but easy to follow guide on water disinfection.
Our Guide to Healthy Travel contains a summary of some water purification methods, including when and how to use them.