You'll never really value a means of Emergency Water Purification, until you've run out of drinking water while sitting next to a body of fresh water, with no way to filter it. You could take your chances and drink it. But several microorganisms, such as E-Coli, Salmonella, and Giardia, that could make you violently ill if ingested, exist and sometimes thrive in these water sources.
They are most prevalent in lakes, ponds and stagnant pools. Stagnant water acts like an incubator for these microorganisms and gives them a place thrive. Running streams and fast moving water are the safest bet, but there are still risks. You don't know if there is anybody upstream from you contaminating the water or if there is a dead animal sitting in the stream just over the ridge. Its just better to be safe than sick. And being sick in the backcountry is a whole different game, you're on your own!
There are several different methods you can use to purify a water source and remove the microorganisms. I've listed the most common methods below, or at least the ones I'm familiar with.
Boiling water for 10 minutes will kill all of its bacteria and microorganisms. This is easiest and most effective way to purify water in an emergency, if you don't have a filtration unit. All you need is a pot and a fire. On the mountain, this is the method we use to purify our water that we use for cooking dinners or having coffee. Hand pumping our drinking water is a time consuming and sometimes strenuous choir. A little extra boiling keeps us from using up our hand pumped, purified water that we depend on to get us through the night.
I can't think of a reason why everyone shouldn't have one of these. They are light, compact and fairly inexpensive, about $100. Ideal for backpacking and taking into the wilderness, but also for filtering water that's been captured in a rain barrel or water from a small pond next to your house.
My hand pump water purifier has 3 levels of purification. The first level is pre-filter, which is essentially a screen to keep moss, dirt and rocks from going into the main unit. Water then passes through a ceramic filtration unit, followed by the final carbon filtration unit. Technically, I only need to pass water through either the ceramic or carbon unit to purify it. So my pump allows me to control the level of filtration. If the water is stagnant, dirty and really sketchy, I will have all 3 levels of filtrations active, but it pumps slow and takes more effort. If the water looks clean, is coming from a fast moving stream, from underneath a glacier, I'm not to concerned and can shut off a level so it pumps faster.
Hand Pump Assembly
Pre-Filter & Float
Ceramic (Left) & Carbon (Right) Filters
I usually run out of time, before I run out of things to do. That seems to be the case both on the mountain and at home. If I can set things up to automate work for me, I'm way ahead of the game. That's exactly what a gravity filtration system does for me at my house.
A gravity filter is exactly what it sounds like. It uses gravity and the weight of the water, to push contaminated or unfiltered water through filter cartridges to purify the water. Its a hands free, no pumping required process. Gravity filtration units are too large and awkward to consider taking into the mountains, but are perfect for emergency water purification at home or in a trailer.
Simply mount the gravity filter unit to the side of your house (or use the included stand) and then attach it to your homes rain gutter system. It's an automated filtration process to convert rain water to drinking water. Connect the output of the gravity filter unit to a fresh water tank or use it to refill your 5 gallon water bottles.
Iodine drops and tablets is another method used for emergency water purification. You add the iodine drops or tablets to a questionable water source, let it stand for approximately 30 minutes and it will kill all of the harmful microorganisms. I always have a bottle of iodine drops or iodine tablets in my backpackers and home first aid kit. The bottle is small and compact, about the size of half your pinky, and it costs about $10.
In fact, Iodine has many benefits and should be in everybody's first aid kit. It not only kills the bacteria and viruses in your water but also within your body. Iodine is a natural antibiotic, antiseptic and antiviral substance.
The technology seems simply enough. You insert a UV light bulb into a questionable water source, turn it on, wait 30 seconds or so, and the UV light kills the microorganisms in the water. My experience with this technology was not a positive one.
As you might have gathered, I tried to stick to the positives regarding each one of these methods. It's very important to familiarize yourself with the downside that each one of these methods possess by reading about Emergency Water Purification Issues and Drawbacks.