There is the rule of threes for survival, which says you can go three minutes without air before you’re dead, three days without water, and three weeks without food. That’s not exact science, of course, and there are variables. Someone in great shape can last longer, and a moderate climate will let you go longer without water. In my part of the world, it gets really hot in the summer, and I suspect three days might be optimistic. Luckily, down here in the southeast, it rains a lot, especially in the summer. There is also a lot of standing water, even during the dry season. The problem with standing water is what’s in it. I don’t know about you, but the thought of drinking diluted duck poop is not a good one. In a crisis situation, there will probably also be people poop getting into the water, and that is far worse than duck poop. There is also a lot of road runoff filled with tire scrapings and oil drippings from cars.
So, what is there to do? I have been worrying about this for years, and that led me to store a bunch of water. However, that is going to run out faster than I would like. I also store pool shock , also known as calcium hypochlorite. With this white powder, you can make a lot of liquid chlorine, and chlorine will make water safe from disease-causing bugs. Don’t forget that if you decide to store some, it is highly corrosive. I have rusty tools to prove it. It is best stored outside, well away from anything you care about. The plastic bags it usually comes in also deteriorate, so you have to replace it every couple of years. You can use it to make enough bleach to whiten everything you own several times over, or if you have a pool you can use it for its intended purpose. When you buy pool shock, be sure you get the stuff that has nothing but calcium hypochlorite in it. Some have extra chemicals that make pools nicer, but you might not want to drink those additives. Drinking chlorine also has some drawbacks for me. I’m not crazy about absorbing chemicals, and the stuff tastes bad. You can, at least, let it sit for a while and the chlorine will diminish.
Another option is something called SODIS , which stands for solar water disinfection. I don’t know why there isn’t a W in SODIS, but I think the UN might have been involved in spreading the program. The idea is that if you put nasty water into the right sized clear polyethylene terephthalate (PET) bottles and set them in the sun for six or so hours, the combination of heat and ultraviolet light will pretty much kill all the bad stuff. The bottle must be made of a material that passes UV light, and the clear PET bottles that most bottled water arrives in works just fine. A lot of glass will stop UV, and any color in the bottle is bad. If the bottles get scratched or discolored, they won’t work well, either. I do recognize that many dislike drinking from plastic bottles, especially when they are heated. This is an equation of balancing competing harms, I’m afraid. I don’t like drinking from plastic either, but it beats getting sick immediately.
There are some limitations, of course. SODIS works best if you are between latitude 35 degree north and 35 degrees south. The northern line equates to the border between North and South Carolina. Further north than that and you start losing efficiency and need to let it sit longer. Rain and clouds also cause issues. Having endured over a week of heavy rain lately (averaging more than an inch a day), I’m happy to have not needed SODIS at the moment. Nonetheless, it is still a viable method and another one preppers should know about. It works best when the bottles are laid on a reflective surface. Many people use a piece of steel roofing, sometimes covered with foil to make it brighter.
While SODIS kills bugs, it doesn’t remove chemicals or particles in the water. You need to let it settle or filter it to get the particles out, as they inhibit the action of UV and sunlight on the water.
A traditional method of treating water is boiling. It works very well but requires time and fuel. It is certainly in my playlist, but I see it as having limits. Among those limits is the fact that it doesn’t remove chemicals or particles. Thankfully, there are solar ovens like the All American Solar Oven I reviewed last year  that can treat water without having to burn fuel, as long as there is enough sunlight.
Besides chlorine, you can get water treatment tablets, like the Katadyn Micropur  ones. They cost $13 for a pack of 30, and each one can render a liter of water safe from bugs. In the worst case, they take four hours to do the job. I have not used them, but they claim the water will taste okay. Some similar products make it taste pretty bad. They advise the shelf life is five years.
A problem with chemical and heat methods is that they don’t remove particles in the water. Some stuff just won’t settle out, so you may be drinking cloudy or colored water, which is disconcerting at best. Things that make water unclear can also make it unpalatable, and that’s where filters come in. I am also a firm believer in redundancy and have become convinced that if one can double treat water, you are probably a lot better off. That meant I wanted something more for our water needs, so I began looking at water filters.
The gold standards for base camp use are the Berkey  and Katadyn gravity filters . You pour water in a tank, and it trickles through ceramic filters with tiny little pores small enough to keep out everything but some viruses. You can also add activated charcoal elements that remove many chemicals including the chlorine I dislike so much. The problem here is the phrase “base use”. I wanted something that we could easily carry if we had to evacuate. The additional use for camping came to mind as well. My son is a Scout and may need it for that in the future. That means I wanted to find something portable, and the big gravity filters, while wonderful for base use, aren’t all that portable, especially on foot.
So again I wondered what to do. Turning to the Internet, of course, and spending many hours in the middle of the night doing research led me back to the first thing I thought of– the Swiss-made Katadyn Pocket Water Filter . At least all that research convinced me it was the right choice for my needs. I had been put off by its $288 price, but I finally concluded that its reputation and features made it worth the money, assuming that one needs portability in the equation.
The first concern I had was the life of the filter. This one is rated for 13,000 gallons, assuming that one doesn’t try to filter mud. I found a number of other alternatives that cost less and worked just as well in terms of getting out bugs, but they simply didn’t have the life of the Katadyn. The size of the unit is fine, 13x4x2 inches contained in its case with attachments, though the weight of all of the above was a bit heavier than desired, at 25 ounces. The promised ability to pump about a quart a minute of water wasn’t bad, either. Faster would be better, of course, but this means we could get the gallon a day per person our family needs in under 15 minutes with some left over for the Dachshund. The 20 year guarantee on the thing didn’t hurt either.
You can get a replacement filter  for $165. One drawback of any ceramic filter is that like anything ceramic, it can be damaged if dropped. Be careful with it or bad stuff will go through a crack. You can extend the life of the filter by cleaning it with an included pad when the water flow starts to slow down from particles clogging the pores.
This filter can remove everything down to .2 microns, which is really quite small. That means it will remove bacteria and germs along with protozoa from water. Protozoa, like giardia lamblia and cryptosporidium, cause serious gastrointestinal issues and are commonly acquired from bad water. E coli, salmonella, and cholera are bacteria-based diseases also ingested in contaminated water. Things are bad enough now, but should there be a crisis, it is hard to imagine how much more contamination will get into water. The filter is also impregnated with silver to prevent the growth of bacteria on it.
The filter also removes turbidity which is, to the simple minded like me, essentially dirt and junk in the water that makes it cloudy. The dirt can provide a place for bad critters to grow, so at some point it needs to go. You don’t, however, want to run anymore dirt than you have to through the filter, so you should let cloudy water sit for a while so as much of the dirt as possible can settle. It is then a good idea to filter it through something like a coffee filter or fine mesh cloth to get as much more out as you can before you run it through the Pocket Filter.
Once you have run the water though the Pocket Filter, please note that it is not effective against all viruses nor does it remove chemicals. Katadyn publishes a helpful card  to provide guidance on what each type of filter and water purification method can do. They also have a very informative guide to water  in general that is well worth downloading and reading, whether you have one of their filters or not. Both explain these points and have led me to the conclusion that I want a multi-step process in preparing water if possible.
My plan is to let the water settle for a good while and then run it through some sort of simple filter. Next, I want to kill all the bad stuff, and that means chlorine, tablets, boiling, or SODIS. Having all four available is best, but in a long-term, grid down scenario, SODIS may be the most sustainable. All it needs is sunlight, but with the vagaries of that, it would be wise to be able to treat a bunch of water when the light is good and then store a lot. In other words, have a good supply of bottles on hand. If you live in the far north, this isn’t going to work as well for you as it will for me. I did decide that two days of treatment would be even more insurance than one.
Once that’s done, I want to filter the water through the Katadyn. While you have killed the bad bugs, the water still may not be sparkling clear, and you have a bunch of dead bugs floating in it. Dead bugs don’t seem appetizing to me, and some argue it is best to remove them. I’m not a biologist and can’t offer any definitive comment other than my gut feeling that I would rather not drink them, so it is best to get rid of them along with all the floating particles of dirt and what not. It is also extra insurance. Getting sick in a survival scenario is not a good plan.
At this point, our water should be clear and free of critters that want to make us sick or even kill us. It may still, however, taste bad. I have, in fact read a number of complaints of a bad taste being imparted by these filters, but a bit more on that later. We could still have chemicals in it. Charcoal filters can help with both issues. Activated charcoal is the best form of the stuff, though plain old charcoal can be used as well. It is just far less efficient at adsorbing bad stuff. The word is adsorption, by the way, not absorption. The end result is about the same, the stuff we don’t want stays in the filter, but the process is different. Adsorption means the filter material attracts what we are trying to capture and latches onto it rather than just holding it as an absorbent filter does.
Activated charcoal is wonderful at capturing organic chemicals, like chlorine, that many people object to consuming as well as many things that make water taste bad. These filters are the basis of many of the systems people buy to make their water taste better and are often found in refrigerators that make ice and dispense drinking water. Some of these have some silver in them to prevent growth of bacteria in the filter. Such filters usually have a life expectancy in time as well as gallons. Six months seems typical. Katadyn offers just such a filter  for the Pocket Filter and some of their other filters as well.
We do, finally, hit a point of not being able to get everything out that can hurt us, primarily in the area of chemicals. We can obtain specialized filters from the home store or Amazon that will remove many other chemicals, but at some point we have to realize we can’t get it all. That frustrates me, but then I realize that it is true of most municipal water supplies and even the bottled water many people buy. We have to do the best we can and motor on.
At this point, I finally got around to trying the filter. We found that the speed of making clean water was a bit optimistic for my family. I could push a liter through in about 70 seconds, which is 10 more than the advertising. It takes effort to work the pump, but it isn’t awful. It is easier than milling wheat with a hand mill. It would be a major chore for one person to try to produce all the water for a family, so plan on switching off.
Out of curiosity on the taste issue, I ran some tap water through it. Sure enough, the flavor did change. It wasn’t as good. It is hard to put my finger on how it changed, but it was still perfectly drinkable. When I added the charcoal filter, it returned almost to the normal flavor. I tried some assorted standing water from around the house, and some of it tasted awful. I suspect it tasted awful before going through the filter, however. In all cases, the charcoal filter made a major improvement to quality. I highly recommend that you get one.
The charcoal filter comes with two refills. You unscrew the thing and pour in the contents of a package. I found the package had more than the filter could hold, so eventually, if you save the remnants, you will have enough for an extra change. The refills  go for $15 for two, and each is supposed to be good for 60 gallons. You should replace it every six months, even if you use less water. Since the refill is powdered activated charcoal , I suspect you could buy a pound of that and save some money, but you would want to keep it tightly sealed, since it can adsorb things from the air too.
A key question in all of this is, would I drink lake water run through the Katadyn without any other of the other steps. The answer is absolutely “Yes!,” if that’s all I could do. The biggest threats to health in water are bacteria and protozoa, and the Katadyn should get them. I would be uncomfortable about it, but I would drink if I were thirsty. I would look for the clearest spot to draw it from and look around for anything that might be contaminating it, like a body or garbage.
Given how hot is here most of the time, I expect to be thirsty most of the time, so this filter makes me a lot happier about my preps. I am still adding PET bottles, maintaining my stock of pool shock, and planning to add some tablets , and more fuel for the various stoves when I can.
– SurvivalBlog Field Gear Editor, Scot Frank Eire  mount