While you may come across fresh, clear water many times on your travels, care must be taken to avoid becoming sick when drinking it. Microscopic bacteria is often found in fresh water stream and rivers, especially near civilization or agricultural areas (farms). Even slight contamination of a water source can leave you violently ill. Fortunately, there are multiple ways to treat suspected water.
- Boil the water for at least 10 minutes, even though 15 to 20 mintutes are recommanded to reduce the risks. This is one of the most surefire ways to purify water, but tends to require lots of patience for sure and fuel (if you don't have a wood cooker).
- Leave it exposed in the sun (with lemon juice) in a transparent bottle. According to some recent studies, leaving water exposed to sun should take 6 hours before being drinkable, and reduced to 30 minutes if adding lemon. Read this article.
- Water filtering. Personal water filters have become commonplace among hikers to ensure that their water is safe to drink. For the average traveler, however, they may be bulky and expensive.
A cheap way of filtering water, although much more time consuming than industry-made filters, is to do it with wood. Follow this link to learn a bit more about it. Using a soft bottle you could as well make a cork out of wood fitting the hole of your bottle. The water will make the cork swell and be blocked in the hole. Now by putting pressure on the bottle, the water will be filtered through the wooden cork, eliminating most of the bacterias. Pine trees seem to be one of the best to filter.
- Chemical treatment. From simple household bleach, iodine, chlorine, or similar chemicals to two-part time-sensitive compounds, chemical purification can offer a small, light-weight and inexpensive option to ensure water purity. Many chemicals can leave water with a slight aftertaste, which can be removed by adding a small amount of powdered drink mix or similar flavoring. When using chemical compounds, it is important to follow manufacturer guidelines, as many of these chemicals are poisonous if misused. A personal favorite of 'Stove' is "Aqua mira", either in a two part liquid or a small dissolvable pill. Liquid to treat 120 liters costs approx $10. However, this is not recommanded for long-term use.
Otherwise you must consume plastic en masse by buying new bottles and be careful that they are well sealed. As well avoid ice put into drinks if you don't know how they are made. If the ice blocks of your Tequila Sunrise are made with bad water, you might end up with more than a hangover.
Water can be unsuitable for drinking for another reason: the cities are too big and not well enough equipped, and water is treated with enough chemicals to make it bad for long-term drinking, even though it cannot really make you sick. In this case bottled water is your only option... For short stays it is not really a problem