If you are hiking or camping in the wild, water quality in the lakes, rivers, and streams can vary widely. This is especially true if you are planning an excursion in a developing country. In some water sources there are typically up to three types of disease-carrying organisms that can’t be seen by the human eye. These are viruses, protozoa, and bacteria. When you are choosing whether to use a water purifier versus a filter, it is important to note that a mechanical, electronic, or chemical water purifier will eliminate all three, while a filter will only take care of protozoa and bacteria.

In most of Canada, America, and in many European countries the risk of viral contamination is considered low enough that water filters will work well for backcountry travel. But in less developed countries and even a few of the world’s leaders…the surface water and even some of the tap water in urban areas can be unsafe to drink. Wherever you plan to travel and hike, check the local water quality or err on the side of caution and treat natural water sources with a purifier.

As an example, here is a blog on the safety of the water in France.