Drinking contaminated water is one of the most common causes of illness when traveling, including travelers’ diarrhea, according to the Centers for Disease Control and Prevention (CDC). Many people reduce this risk by buying bottled water, but even bottled water is not always adequately treated and could in some cases be plain tap water, according to the Food and Drug Administration (FDA).

Buying bottled water also contributes to a host of environmental problems:

  • More than 250,000 tons of plastic is floating in the world’s oceans, according to a scientific study published in the journal Plos One.
  • In the United States, more than 60 million plastic bottles are thrown away every day, according to the Container Recycling Institute, a non-profit dedicated to increasing recycling. Only 13 percent of our water bottles are recycled, the Natural Resources Defense Council (NRDC) says.
  • It takes three liters of water to produce and package one liter of bottled water, according to the Pacific Institute, a global water think tank.
  • The fossil fuels burned to produce and transport plastic water bottles contribute to global warming. In fact, the NRDC says shipping water bottles to and from U.S. ports creates thousands of tons of global warming pollution and other air pollution.

Related: Plastic: A Bunch of Seriously Good Reasons to Just Say No

If you’re traveling, there are numerous alternatives to bottled water that are both healthy and environmentally friendly.

Boiling water

Boiling water is a simple and effective way to purify drinking water. Boiling gets rid of virtually all pathogens and does not affect taste. Heat water at a rolling boil for at least one minute or three minutes at high altitudes, the CDC says.

Mechanical filters

Mechanical water filters use hand pumps and gravity to remove solids. Size determines the filter’s effectiveness. An “absolute” pore size of 0.1 to 0.4 micrometers (µm) is usually effective against protozoa and cysts (tiny parasites such as cryptosporidium and giardia), as well as bacteria (including E. coli and salmonella). It is not effective against viruses like hepatitis A.

Mechanical filters do not require batteries and are generally rugged in their construction. “This type of filter really comes in handy when you know you will be drinking out of a water source with particulates and need to remove them or if you won't be around any electricity,” says Jonathan Burnham of the Travelers Against Plastic (TAP) campaign, an outreach initiative that encourages travelers to adopt alternatives to plastic water bottles. A downside to mechanical filters is their size, as well as the physical effort involved in operating the hand pump.

Related: Why You Should Break Your Bottled Water Habit

Chemical disinfectants

Treating water using chemicals such as iodine or chlorine dioxide is very effective against bacteria and viruses, but it has little impact on most protozoa and cysts. It also does not work well on water that is muddy or contains particulates.

Chemical disinfectants come in tablet or liquid form and are lightweight and simple to use. Just drop them in the water and wait. Disinfection usually takes about 30 minutes, though in areas where cryptosporidium is a risk, the recommended treatment time can be as long as four hours.

If you don’t like the taste of chemically treated water, adding a neutralizing tablet of vitamin C can help remove the unpleasant taste.

The CDC recommends a combination of filtration and disinfection as the most effective way to treat water without boiling.

Related: For Clean Drinking Water, Take a Page Out of This Book

Ultraviolet (UV) light treatment

UV-light purifiers zap pathogens and render them unable to reproduce and cause illness. Portable, battery-operated versions, like the SteriPEN, are ideal for travel because they are compact, lightweight and easy to use. “I‘ve used mine in 15 countries and have even gone so far as to drink well water in Morocco with and without treating the water,” says Burnham. “I didn't get sick when I treated the water but did when I drank it without purifying it first. Proof that it works.”

UV purifiers work quickly. The down side: They need to be recharged occasionally, and the quartz lamp that emits the UV light is fairly fragile. Also, UV treatment will not work well if water is murky or gritty, so carrying a small prefilter strainer is a good idea if you think you might come across water that contains particulates.

Good reusable bottles

Whatever treatment method(s) you choose, you’ll need a reusable water bottle. Stainless steel and aluminum bottles are good choices, as are bottles labeled BPA (bisphenol A) free. Beware of reusing disposable water bottles, as the plastic can break down and attract bacteria.

Some water bottles come with built-in filters. Examples include the Grayl Water Filtration and Purification Cup, which works like a coffee press, and the CamelBak All Clear Bottle, which has a built-in UV light purifier.

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Annika S. Hipple is a travel consultant, tour leader, freelance writer and photographer specializing in travel and sustainability. The former news editor for Ethicaltraveler.org, she has also contributed to Sierra Magazine, Earth Island Journal, the Christian Science Monitor, the Seattle Times' Trip Magazine and many other print and online publications.