Portable water purification devices are small, easy-to-carry tools used to clean water from natural sources like rivers, lakes, and wells so it can be safely drunk. Their main purpose is to remove harmful germs, as well as tiny particles and some substances that may taste bad or be dangerous.

These tools help people who do not have access to clean water, such as those in areas with limited resources, disaster zones, soldiers, campers, hikers, workers in remote areas, and survivalists. They are also known as point-of-use water treatment systems and field water disinfection methods.

Common methods used by these devices include boiling water, filtering water through special materials, using activated charcoal to trap impurities, adding chemicals like chlorine or iodine to kill germs, using ultraviolet light (such as solar disinfection), boiling water to create clean steam (distillation), and using a process called flocculation to gather dirt and particles together. These methods are often used together to ensure water is safe to drink.

Drinking water hazards

Untreated water may contain disease-causing organisms, such as protozoa, bacteria, viruses, and larvae from parasites like liver flukes and roundworms. Chemical pollutants, including pesticides, heavy metals, and synthetic chemicals, might also be present. Other substances can affect the water’s taste, smell, or appearance. For example, turbidity (cloudiness) can come from soil or clay, color from humic acid or algae, odors from certain bacteria like Actinomycetes (which produce geosmin), and saltiness from saltwater or brackish water.

Common metal contaminants, such as copper and lead, can be removed by raising the water’s pH with soda ash or lime, which causes the metals to settle out. Carefully pouring off the clear water after settling or using filters can reduce metal levels to safe amounts. However, water contaminated with aluminum or zinc cannot be treated this way, as higher pH levels may dissolve the metal salts again. Removing salt is difficult except through reverse osmosis or distillation.

Most portable water treatment methods focus on removing harmful germs to ensure safety and reducing particles, tastes, and odors. Common pathogens in developed countries include Giardia, Cryptosporidium, Shigella, hepatitis A virus, Escherichia coli, and enteroviruses. In less developed areas, risks may include cholera, dysentery, and tropical parasites.

Giardia lamblia and Cryptosporidium species, which cause diarrhea, are often found in untreated water. In some wilderness areas of the United States and Canada, these germs may be present in amounts that justify water treatment for hikers, though this practice has sparked debate. In tropical regions like Hawaii, Leptospira species may also be a concern.

In developed countries, organisms like Vibrio cholerae (which causes cholera) and Salmonella (which causes typhoid and paratyphoid) are less common. Viruses can also be found in water. The larvae of flukes are dangerous in areas near sheep, deer, or cattle. If ingested, these larvae can form harmful cysts in the brain or liver. This risk also affects plants like watercress grown near water sources.

Generally, the more human activity upstream (such as in larger rivers), the greater the risk of contamination from sewage, runoff, or industrial waste. Groundwater pollution can result from human actions, like poor sanitation or mining, or occur naturally, such as arsenic in parts of India and Bangladesh. Collecting water as far upstream as possible, away from pollution sources, reduces contamination risks and makes it easier to treat with portable methods.

Techniques

Not all methods can stop all dangers. Even though flocculation followed by filtration is often suggested as the best practice, it is rarely possible without carefully controlling pH and settling conditions. Using alum as a flocculant without care can lead to unsafe levels of aluminum in treated water. If water is to be stored, halogens provide long-term protection.

Heat kills disease-causing microorganisms, and some require higher temperatures or longer time to be destroyed. Sterilizing water (killing all living germs) is not needed to make it safe to drink; only making intestinal pathogens harmless is required. Boiling does not remove most pollutants and does not leave any lasting protection.

The World Health Organization (WHO) says that bringing water to a rolling boil and then naturally cooling it is enough to kill harmful bacteria, viruses, and protozoa.

The Centers for Disease Control and Prevention (CDC) recommends a rolling boil for 1 minute. At high elevations, though, water boils at a lower temperature. At altitudes above 6,562 feet (2,000 meters), boiling should continue for 3 minutes.

All bacterial pathogens are quickly killed above 60 °C (140 °F). Even though boiling is not needed to make water safe to drink, the time it takes to heat water to boiling often reduces bacterial levels to safe amounts. Encysted protozoa may need higher temperatures to fully remove any risk.

Boiling is not always needed or enough. Pasteurization, where enough pathogens are killed, usually happens at 63 °C for 30 minutes or 72 °C for 15 seconds. Some pathogens must be heated above boiling, such as botulism (Clostridium botulinum requires 118 °C (244 °F)), most endospores (120 °C (248 °F)), and prions (even higher). Higher temperatures can be achieved with a pressure cooker. Combining heat with ultraviolet light, like the SODIS method, reduces the needed temperature and time.

Portable pump filters with ceramic elements are available. These filters can process 5,000 to 50,000 liters per cartridge and remove pathogens as small as 0.2–0.3 micrometers (μm). Some also use activated charcoal. Most filters remove most bacteria and protozoa, like Cryptosporidium and Giardia lamblia, but not viruses unless they are larger than 0.3 μm. Disinfection with chemicals or UV light is still needed after filtration. It’s important to note that not all bacteria are removed by 0.2 μm filters; for example, Leptospira spp. (which cause leptospirosis) are thin enough to pass through. Effective chemical additives to improve filter performance include chlorine, chlorine dioxide, iodine, and sodium hypochlorite (bleach). Some filters once used iodine in their elements to kill viruses and small bacteria, but these were rarely used due to the unpleasant taste and possible health risks from long-term iodine use.

Filtration elements may remove most bacteria and fungi when new, but they can become places where germs grow. In recent years, some filters have been improved by adding silver nanoparticles to ceramic or activated charcoal elements to reduce pathogen growth.

Small, hand-pumped reverse osmosis filters were first made for the military in the late 1980s as survival equipment, such as for use with inflatable rafts on aircraft. Civilian versions are now available. These devices use a hand pump instead of water pressure to force water through the filter and can produce drinkable water from seawater.

The Portable Aqua Unit for Lifesaving ("PAUL") is a portable ultrafiltration-based membrane filter used for humanitarian aid. It provides clean water for about 400 people per day in emergencies and disasters. It works without chemicals, energy, or trained personnel.

Granular activated carbon filters use activated carbon with a large surface area to absorb many compounds, including toxins. Water passing through activated carbon is often used with hand-pumped filters to remove organic contamination, taste, or odors. Activated carbon filters are not usually the main method for portable water purification but are used as a secondary step to complement other methods. They are often used before or after ceramic filters and before adding chemical disinfectants. Activated charcoal can remove chlorine from treated water, which might reduce protection against pathogens, so it should be used carefully after chemical treatments. Ceramic/Carbon Core filters with a pore size of 0.5 μm or smaller are good at removing bacteria, cysts, and chemicals.

Chemical disinfection with halogens, mainly chlorine and iodine, works by breaking down essential parts of microorganisms. The main factors affecting how well this works are the amount of halogen in the water and how long it is exposed. Other factors include the type of pathogen, water temperature, pH, and organic contaminants. In field conditions, using 1–16 mg/L of halogen for 10–60 minutes is usually effective. Note that Cryptosporidium oocysts, Cyclospora species, and Ascaris eggs are very resistant to halogens, and inactivation may not be practical with bleach or iodine.

Iodine for water purification is added as a solution, crystals, or in tablets that release 8 mg of iodine each. Iodine kills many, but not all, common pathogens in natural freshwater. Iodine is a lightweight but imperfect solution for field use. Camping stores sell kits with iodine pills and vitamin C or ascorbic acid pills to remove the iodine taste after treating water. Adding vitamin C removes iodine from the solution, so it should not be added until the iodine has had time to work. This time is 30 minutes for clear, warm water but longer for turbid or cold water. If iodine has been removed, the water has less available iodine. Tetraglycine hydroperiodide tablets remain effective indefinitely before opening; some manufacturers suggest not using them after three months, but their shelf life is long if the container is resealed after each use.

Like potassium iodide (KI), enough

Prevention of water contamination

Water-borne diseases in humans are often spread by other humans. To prevent contamination, materials from humans, such as feces, medical waste, wash water, lawn chemicals, gasoline engines, and garbage, should be kept far away from water sources. For example, human waste should be buried more than 60 meters (about 200 feet) from water sources to reduce the risk of pollution. In some wilderness areas, it is advised that all waste be collected and taken to a proper disposal location.