Drinking water safety: it's one of those things you might not think about until you're locked in the bathroom feeling like the world is ending. Making sure your drinking water is safe is a foundational part of travel - you can't just wing this one.
Maybe I should have called this page How to avoid Montezuma's Revenge... although drinking contaminated water can make you far sicker than that.
Clean drinking water is something we take for granted at home and if you're heading for a Western country you should be just fine drinking the tap water.
If you're going to a developing country, however popular with travelers, find out about the water before you drink it.
According to the World Health Organization, 80% of all travel disease is the result of contaminated drinking water.
I would distrust tap water in most developing countries and even some not-so-developing ones in Africa, South and Southeast Asia, the former Soviet Union and much of Central and South America. The map below will give you a better idea of what to expect.
Just to make things a bit more confusing, some countries may have perfectly safe drinking water in the capital, major cities and resorts, with water undrinkable everywhere else. Always ask someone local, or look it up before drinking.
If you have any doubt at all about the tap water, don't drink it. In fact, don't dring ANY water you don't trust. But what can you drink?
There are plenty of options, some better than others.
There's obviously bottled water but you can also boil your water, treat it chemically, use UV light on it or filter it physically. Lets look at the pros and cons of each of these.
Drink bottled water
This is often the simplest solution but it comes at a cost - financial, of course, because bottled water can be quite expensive, but there are other costs as well. Two weeks' travel for one person could mean at least 21 one-liter bottles to dispose of - and that's if you only drink a liter a day and use half a liter for all your other needs.
Before treating your contaminated water, make sure you eliminate any sediment in the water by straining and filtering. Choose the cleanest water, preferably flowing, not stagnant.
Put the kettle on
A cheap option is to boil your water but be sure to let it boil at length. Some people say one minute is enough unless you're at a high altitude but I don't take any chances and let it boil longer. Before you boil make sure you filter it and get rid of any sediment or specks you can see. Then let it cool before drinking (skip this step at your own risk - and find out what a tongue blister feels like). Or why not make a nice cup of tea or coffee with that boiled water?
That said boiling isn't always feasible or convenient.
Taking the tablets
These can be made from a variety of chemicals: silver ions (no taste but traditionally used for water cisterns in boats or campervans), chlorine bleach (mostly effective but tastes and smells awful), chlorine dioxide (much less yucky and in a pinch can be used in cloudy water) and iodine (doesn't kill everything but must not be used over any length of time because it's harmful to your body).
The problem with iodine and chlorine (bleach) is that they also exist in strengths never intended for water purification. Using these can lead to overdose and death. To keep safe use products sold solely for water purification and follow their instructions to the letter. Take note: iodine is dangerous for pregnant women, if you have thyroid problems, and a few other conditions so read up about it.
When traveling to places like the Brazilian Amazon or Indonesia, I've tended to use tablets like Micropur or Potable Aqua tablets (though I've decided to test a UV purifier on my upcoming trip to Borneo).
You'll use more tablets than you think so calculate properly: some doctors recommend drinking between 2-6 liters (very roughly 4-12 pints) of water each day so a small pack of tablets won't go very far and they're quite expensive.
It's not just the water, it's also the food
You don't have to die of thirst: drink reputable packaged fruit juices, sodas, sparkling water, coffee or tea, since boiled water is safe. Beware of pressed fruit juices though: they might be diluted with tap water, sugar is a breeding ground for bugs, hands and machines must be kept clean... not an easy task so I'd skip them if you're uncertain.
Beware of cocktails - they could have water, ice and those iffy fruit juices. You'll be pleased to know wine, beer and spirits are safe when it comes to water (although dehydration and drunkenness could be side effects). Please note: alcohol drunk after ingesting dirty water will not retroactively kill bugs.
More water purifying options: zap those bugs dead with UV light
The top of the line are purifiers that use ultraviolet light, which can get rid of almost anything, even viruses. They don't use chemicals (I like products that help me avoid them), and they tend to be easy to use. The most popular, according the reviews on Amazon (and almost everywhere else) is the SteriPEN: just stir clear water with the wand and it kills pretty much everything that's bad for you. It's light and easy to carry and uses AA batteries, which you'll find almost anywhere. I haven't tried it yet but I'm buying one for my upcoming Borneo trip. I do know plenty of travelers who swear by it so I'll be guided by them. To be on the safe side though - things do break - I'll also take along some tablets.
One thing though - and this is boring, but probably the most important thing you have to do is read the instructions! Otherwise you may end up drinking dirty water that will make you sick.
The physical water filter
A popular brand is the Katadyn Water Bottle, which filters and purifies water as you drink it. Cool, that, and great for solo travelers. If you're headed on a longer trek in inhospitable territory (with filthy water), you'll want the Endurance range. If you don't expect the water to be that dirty, the Backcountry series should do the trick. And if you're headed for a short-ish trip with light purification needs, the Ultralight will be all you need. (One filter can only purify 100 liters, and much less if you've been filtering filthy water.)
(This selection from Amazon shows you which bottles have the most customer reviews - read them and decide.)
Stranded, dying of thirst and have absolutely nothing with which to purify or clean water? You can take a chance and strain water through your T-shirt and take a tiny sip, but be warned: it could make you very ill.
I was in a similar situation in the Brazilian Amazon some years ago - plenty of water in the river, but nothing with which to purify it, not even a fire for boiling. Desperate with thirst I did exactly that, used my T-shirt. I was lucky and nothing happened but I shudder each time I remember that day because I could have gotten extremely ill.
Make sure this never happens to you: be equipped.
Before you use any purifiers, whether filters or pills or anything, make sure your water is as clear as possible. A T-shirt will help, but so will a bandanna, a coffee filter, or anything similar you have at your disposal. As for bottles, you could also use a stainless steel bottle or special plastic bottles that are manufactured without BPA.
And if you're concerned about spending money on water purification travel products, don't be: you never know when it might be of use to you. Keep the gear somewhere safe because if your home water supply goes down for some reason or your area is affected by some kind of natural disaster, you might be awfully happy you bought a quality water filter.
If you're a hard-core trekker and spend a lot of time outdoors, splurge and get one of the more expensive options: they'll last longer, you'll have to replace consumable parts less often, they'll be available for longer, and you'll get a better guarantee.
Whatever you buy, get a backup in case your primary water purifier fails.
And don't forget to test any equipment before you go! You want to know how it works and if there's a problem while you can still solve it.
Since this isn't a medical site I won't give you any medical advice, but you do need to take any water or food-related illness seriously, especially in a hot dehydrating climate.
How will you know if you're sick because of the water? You'll probably develop nausea or vomiting, you may have a fever or diarrhea, and you might feel aches and pains, or stomach cramps. If your diarrhea is bloody or you have a fever, I'd get to a doctor right away. This is even more important if you're elderly or have special health problems or if this happens to an accompanying child.
If getting to a doctor immediately isn't an option, rehydrate! Drink plenty of clear fluids or better yet, use oral rehydration salts (ORT). I always carry a few packets when I travel, just in case.
No ORT? Don't worry, the mixture is easy to make: take 1 liter - about 5 cups of bottled or sterilized water, and add 1 teaspoon of salt and 8 teaspoons of sugar. Drink it slowly, taking little sips. You can easily get these at your mountain or travel shop, or from places like Amazon.
A word of caution though - there is a lot of debate about ORT and like everything you can cause problems in trying to solve them - if you have an imbalance and you're trying artifically to fix it you won't know how far to go. If you have the option, get to a facility where you can be stabilized.
A final word: if you're in the Alps or other pristine environment and you come across a crystalline stream, don't assume the water is potable. A rat, mouse, fox or other animal may have peed in it further upstream. This could make you very ill so purify any water, or play russian roulette with your health.