IAMAT |International Association of Medical Assistance to Travellers| IAMAT |International Association of Medical Assistance to Travellers|

Drinking water safety

In many parts of the world, the water isn’t safe to drink. Human waste from poor sanitation and chemicals like fertilizers are just two common sources of contamination. For many short-term travellers, bottled water seems like the easiest solution, but bottled water creates plastic waste which often isn’t recycled. Bottles can also be tampered with and refilled with unsafe water. Also, for travellers to rural or remote areas, carrying a large supply of drinking water may not be possible.

So what can you do? One option is to treat your own water. Find out everything you need to know about water safety and how to choose the right water treatment method for your trip below.

What’s in the water?

There are many microorganisms and substances that can contaminate drinking water. Viruses that cause Hepatitis A, bacteria like E. coli, protozoan cysts like Giardia and Cryptosporidium, and some eggs and larvae can be found in water worldwide. Sewage and chemical run-off from manufacturing, agriculture, and mining as well as acid rain can also contaminate surface water and wells. In many countries, a lack of or outdated sanitation systems contribute to the water contamination.

Clean water – Where do I start?

Drinking water safety is a common topic during travel health consultations. Water quality can vary from place to place within a country and the method you use to get drinking water depends on your style of travel. There are so many products on the market that it can be tough to figure out the differences between them and which one is the best fit for your trip.

One of the first things to know are some of the terms for methods used in the field to get drinking water (also called potable water).

  • Disinfection: All microorganisms harmful to humans have been removed or destroyed. Water that has been disinfected is safe to drink. Disinfection is the preferred outcome when treating water for human consumption.
  • Purification: Removes unpleasant tastes, odours, and particles clouding the water. Purification may also remove some pathogens, but it’s not reliable by itself to get potable water.
  • Sterilization: All life forms in the water have been destroyed. There is no need to sterilize water to produce safe drinking water.

Disinfection methods

There are several ways to disinfect water.

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. Disinfection methods include the following: 


Boiling your water is an easy one-step method and the most reliable. It is the most effective method for killing disease-causing viruses, bacteria, and parasites. It doesn’t require a thermometer or special tools, just a heat source.

If your water is cloudy, let it settle (so the sediment makes its way to the bottom) or strain it through a coffee filter or clean towel before bringing it to a boil.

Let the boiled water cool before drinking it. You can store it in a sanitized container with a tight cover.


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.

Ultraviolet light (UV)

UV light inactivates viruses, bacteria, and cysts like Giardia and Cryptosporidium. It is a quick disinfection method but is most effective for treating small amounts of clear water.

There are several products on the market for travellers. UV products come with a built-in timer and are generally small and lightweight 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.

Halogens/chemical disinfection

Chemical disinfection is the most common water disinfection method in the world. Chemical disinfection using chlorine, iodine, or chlorine dioxide 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. Boiling water is the most reliable one-step method for water disinfection.

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.

Note that iodine should only be used in short-term emergency situations. Do not use iodine if you are pregnant, have a thyroid condition or iodine allergy.


If your water is cloudy, you can make it clearer by removing particles suspended in it. This includes techniques like sedimentation (letting large particles settle to the bottom) and coagulation-flocculation (using a coagulant like alum to make particles clump together and separate from clear water). Afterwards, you must use a disinfection method, such as heat, filtration, UV, or halogens. Tablets that combine flocculation and chlorine are also available.

Tap water and clear surface water

Tap water in some countries may need to be disinfected due to aging water treatment systems or inconsistencies in municipal water treatment. When treating tap water 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.

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 crisis zones 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.

* IAMAT has no affiliation with the products listed above. Links are included to illustrate the variety of water disinfection products available.

More information

Last reviewed and updated: December 11, 2020.

Image by: Karl Erik Bennion

Travel Health Journal