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water filters and drinking water

Drinking Water 101: What’s in the water?

This is Part 1 of a two-part series on water disinfection. Read Part 2, Drinking Water 102: Choosing the right method for your trip.

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. For travellers to rural or remote areas, carrying a supply of drinking water may not be possible.

So what can you do? One option is to treat your own water. In this post, we’ll take a look at common contaminants and basic methods for making water safe to drink.

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 In many countries, lack of or outdated sanitation systems contribute to the water contamination.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. Depending on the method you choose, getting potable water may involve different steps. Here are some of the most common ones used by travellers that will be discussed in detail in Part 2.

  • Heat: Bring water to a full boil. This one-step method is easy as it doesn’t require a thermometer or special tools.
  • Filtration: Filters are easy to use but can be expensive. They may also let some viruses through so treat water with heat, halogens, or ultraviolet light after filtration.
  • Clarification: Cloudy water is made 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). Water treated with this method should also be disinfected.
  • Ultraviolet light (UV): UV light inactivates viruses, bacteria, and cysts like Giardia and Cryptosporidium. It is a quick disinfection method when sufficient doses of UV light are used and there are several products on the market for travellers. This method is most effective with clear water.
  • Halogens/chemical disinfection: Chemical disinfection includes treating water with chlorine dioxide, chlorine, or iodine. Chemical disinfection is relatively cheap and can be adapted to different quantities of water, but using it requires some understanding of how to scale the dosage up or down. 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.

The CDC’s summary of field water disinfection techniques includes an easy-to-read chart showing which pathogens are susceptible to each disinfection method. Keep in mind that boiling water is the most reliable one-step method for water disinfection.

In part 2, we’ll look at popular water disinfection products and how to choose them based on your travel needs.

* Field Water Disinfection by Howard D. Backer, Wilderness Medical Society, 2009.

By Daphne Hendsbee and Tullia Marcolongo.

Photo courtesy of Karl-Erik Bennion, freeimages.

More information:

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.

Travel Health Journal