With that out of the way, I am here to recommend one of the cooler travel gadgets I've been using this trip. It's called a Steripen. It makes just about any water safe to drink, one liter at a time.
When I first heard about it, I was skeptical. But, before leaving, I asked one of the doctors in my travel clinic about it. She had nothing but good things to say. So, I found one on sale at REI (they're not paying me to write this either), four rechargeable AA batteries with a little solar charger, and I was good to go.
The Steripen looks like a plastic stick with a long lightbulb sticking out of it. The way you use it is to fill up a water bottle with a liter of water, press the button on the Steripen, wait for a flashing green LED light, and then stir it around in your water. The bulb end will light up. After you stir for a couple minutes, the bulb turns off, and the LED flashes green. The water is now safe to drink.
The way it works is that the bulb is a UV bulb. The UV radiation destroys any parasites, bacteria and viruses swimming around the water. It's the biological equivalent of boiling the water for a few minutes, only you don't have to wait for it to cool down after. The water must be clear (no dirt) for the thing to work, and you need to keep it in and stirring the for full period of time or it won't do the job. If you pull it out too early, you'll get an angry little red LED flashing and have to start over.
I have been using this device in seven continents for over a year, and I have not once gotten sick from the water it treated. I trust it with just about any tap water in the world. I will say that it doesn't make the water taste any better, but as long as the water is clear, it can treat it and drink it, (unless it's from one particular cheap hostel in Siam Reap, Cambodia, because that water tastes foul enough to make your stomach turn, even when sterilized).
Bear in mind that this doesn't do anything for water with nasty metals like lead or mercury in it. This is very rare, I've yet to run into it. More common is a few cities where they just dump too many chemicals like chlorine into the water for it to be drinkable in large quantities (so far the only ones I have had this problem with are Moscow, Istanbul, and Damascus) If you're in doubt, ask if the water would be safe to drink after boiling for a few minutes. If so, you can use a Steripen.
The only problems I've run into are with the button itself. After several months in my backpack, the button sometimes doesn't respond to the first press. I often have to try pressing it several times or pressing it very hard in just the right direction to start the thing up. But I just put that down to normal wear and tear, given what it has to go through inside my bag.
This is my answer to the problem of drinking water. The traditional method to this problem is to buy bottled water wherever you go. If you're keeping yourself properly hydrated (which you should be), this causes a huge amount of waste in plastic bottles (most of the developing world, where you'll use them most, can't recycle them). You also have to start getting paranoid about seals and whether bottles you're buying are really just old bottles being re-filled with tap water by local entrepreneurs. Finally, last, and in many ways least, while water is very cheap in places where tap water is undrinkable, it's still an expense that's nice to cut out.
So, my advice? Get a sturdy, 1-liter water bottle, and then go get yourself a Steripen. Now anywhere you have tap water, you'll have safe drinking water.
I'll use this opportunity to point out a little something on the site I'm trying out. I've labeled it (are you ready for the cheesy cheesiness?) the JTrek Store. I quietly put it up months ago on the right sidebar, but never explained it. Here's my explanation:
If you click the link to the store, you'll find a few things, including several models of Steripens. These are things that either I carry or are a lot like things I carry (smaller sizes or womens' versions for example).
You can buy them there. If you want. A very small portion of the price (1% on most items) goes to my trip. The rest goes to Amazon.com and their affiliates. I encourage you to use the store mostly as a reference list-- if you think you can get a better deal somewhere else, go for it. Check your local outdoor and travel stores as well as the internet.
One other thing, I can add anything you can buy on Amazon.com to the JTrek Store. So if, for example, there's something I've talked about that you don't see on there, feel free to suggest it, and I might add it later.
Or, if you want to buy something crazy like a Segway or a car on Amazon and feel like donating 1% of the price tag to my trip, let me know, and we'll get it on the store for you in time for purchase. I kid. Mostly.
Anyway, that's the deal behind the store. I hope it's useful to you and your adventures!