Water from open sources must always be treated before use. The lack of proper attention to water quality can be life threatening. By a review of the literature there appears to be no one way to treat water to make it safe. As I went through the Blog I found numerous authoritative sounding articles that contradicted other equally authorities articles. Unless we can get EPA experts or similar authorities to talk about water quality in WTSHTF  conditions and not 4 acre treatment facilities you have to pick your experts and go with them, understanding that none of us have ever been there.
There are numerous methods for treating water including osmosis, distillation, ultra violet, boiling, filtering, and chemicals such as chlorine or iodine. Most of these treatments are aimed at biological contamination and each of them has disadvantages in a WTSHTF scenario. (Contaminates may also include chemicals but that is beyond the scope here.) I have a preference toward water treatment methods that can be applied in a WTSHTF which eliminates the methods requiring significant electrical power.
What are we trying to do? How to sterilize water? You don’t need to ‘sterilize’ water. Sterilization is the destruction of all microorganisms in, on and around an object. What is needed is disinfection (killing of pathogenic (disease causing organisms). Another proposal is Pasteurization (less than boiling (149°F) but a temperature high enough to “kill disease causing organisms”.) The exception might be Ultra Violet treatments which don’t kill the organism but leave them so they can’t reproduce which makes them harmless.
Biological contaminates consist of microorganisms also called microbes. There are four different groups. Arranged from largest to smallest they are, fungi, protista, bacteria, and viruses. The smallest bacteria which causes human disease is Mycoplasma pneumoniae which is approximately 0.2 microns in size. When selecting a microfilter, I want one that filters down to at least 0.2 microns (a micron is one micrometer or 0.000001 meter or 1 x 10-6 meter). While effective against bacteria and larger microorganisms, even a good microfilters (0.2 microns) cannot be counted on to filter out viruses unless there is another mechanism to trap or destroy the virus. All the viruses I am familiar with are smaller in diameter than 0.3 microns, examples include Smallpox 0.250 microns, Rabies 0.150 microns, Influenza (Flu) 0.100 microns, and Polio 0.028 microns. Viruses are composed of DNA or RNA surrounded by a protein coat called a capsid. This construction allows them to be easily destroyed by boiling or chemicals such as iodine or chlorine (bleach). While iodine or chlorine is effective against viruses, it is ineffective against the protista Cryptosporidium.
(Since the first recorded human case of Cryptosporidiosis in 1976, it has grown to become one of the most common waterborne diseases. In 1993, an outbreak in Milwaukee, Wisconsin infected approximately 400,000 residents. 4,400 people had to be hospitalized and the cost of the outbreak was estimated at over $54 million. If this is a problem now, imagine what it would be in WTSHTF scenario. See the CDC web site  for additional information.)
Unfortunately, some bacteria produce spores which can survive extreme conditions. They can survive being boiled in water (100 degrees Celsius) for two hours, survive in 70% ethyl alcohol for 20 years, or survive one million REM of radiation (600 REM is fatal to most people). One of the most infamous bacteria that form spores is Bacillus anthracis which causes Anthrax.
Unfortunately we don’t know what bad guys are in the water we will get in the future so you make your choices and take your chances. Here are some suggestions that might help you make these choices. It will always be a juggling act between: Time consumed, cost – energy and financial, and what you think you are protecting your selves from.
Many prepper discussions include bleach as a means to add chlorine to the water to be treated but the shelf life has you moving to the dry pool shock (Calcium hypochlorite) as an easier storage item and far more concentrated source of chlorine. (Long term storage of Calcium Hypochlorite still need to be resolved because of evidence of slow generation of Chlorine gas.) [JWR Adds: The main concern is that chlorine gas is corrosive, and will induce rust on any exposed metals that are nearby, even in very dry climates.]
Calcium Hypochlorite – Mixing From the EPA site : “Granular Calcium Hypochlorite. Add and dissolve one heaping teaspoon of granular calcium hypochlorite (~50%) (Approximately 1/4 ounce or 1 heaping teaspoon) for each two gallons of water. To disinfect water, add the above developed stock (bleach replacement) chlorine solution in the ratio of one part of chlorine solution to each 100 parts of water to be treated. This is roughly equal to adding 1 pint (16 oz.) of stock chlorine to each 12.5 gallons (1,600 oz) of clear water to be disinfected.
It is usually recommend that a three step approach to treating water from open sources be followed:
Pre-filtering. This removes particulate matter. Pouring water though a couple of thickness of t-shirts or tightly-woven bath towels or coffee filters works fine. The water that comes through may still look like tea, but at least you have removed the crud and larger particles. By pre-filtering, you will also extend the life of your water filter. (You avoid clogging the microscopic pores in the filter media.)
Chlorinating. (Iodine – Hydrogen peroxide etc) This can be accomplished following directions above
Final / fine – Filtering. The large Katadyn or British Berkefeld filters. Some filter elements available for Katadyn or British Berkefeld filters .2 micron rated. (Complete filter systems and spare filter elements are available from Ready Made Resources,  Safecastle , Katadyn Pocket filter , and other Internet vendors.
Follow up questions needing additional research:
Disease-causing organisms in water are killed by exposure to heat in a process known as pasteurization. Water heated to 65°C (149°F) for a short period of time is free from microbes, including E. coli, Rotaviruses, Guardia and the Hepatitis A virus. A Water Pasteurization Indicator (WAPI) is a simple thermometer that indicates when water has reached pasteurization temperature and is safe to drink. It was invented by Fred Ba rrett  and Dale Andreatta . An article written by Dr. Bob Metcalf who promotes pasteurization at 149°F stated that it kills Guardia but no mention of the Guardia spores which I have read cannot be killed by boiling?
Lot of discussion on the blog about the non-active ingredients in your Calcium Hypochlorite. I have heard some ideas as to what the non active ingredients are and not having an active chemistry expertise have come to the conclusion that if it is going into a pool it has to be pretty close to drinkable and we are diluting the snot out of it. (Am I copping out?)
When using the purchased filters in step 3 for the final filtering how do you know if the filter is functioning? Is it as simple as, when the water will not flow through it, it’s plugged? Is there a way to regenerate them? In the bigger picture, how long after the WTSHTF will your current stock of extra filters last? In my search to understand using pool shock as a source of chlorine I did some minimum reading about pool filters and have to ask if there is a pool filter that is sand based that can be recharged / regenerated mechanically. I try to always look at techniques in two perspectives, short term while stored supplies last and long term, what do you do when your chlorine is gone and all your micro pore filters are clogged. Regenerating a sand filter has a nice ring to it. I have never owned a pool and have no experience with this. Can anyone tell me if this is reasonable? Could this type of filter get you close to the .2 micron goal of the purchased filters
Has anyone looked into the long term storage of Calcium Hypochlorite. It is sold in plastic bags that I fear contain it as well as gunny sacks contain grain dust. Short term answers appear to be glass containers that depend on rubber gaskets. I have seen rubber gaskets become dry, brittle and worthless with no more than just age. Is there a better storage mode?
I am consistently impressed with how dummied down things like mixing Calcium Hypochlorite to make a stock solution of how much of the stock solution to put in drinking water. It leaves me wondering how may preppers reload their own ammunition. If this is a reasonable number, as I think it might be, then we all have access to a very accurate scale and can move to exact measurements vs heaping teaspoons. Is there a reason for not using this cross subject expertise?
I may have just received an answer to some of my question about killing things like giardia cyst. I am still rereading and trying to digest this article . Vinegar anyone?
Addendum: I just got through to a customer rep for PPG, the makers of the Calcium Hypochlorite for the 73% Pool Shock I bought from Leslie’s. He told me that the balance of 27% in this product is NaCl (table salt) and chemically bound water. (This product is used in potable water treatment systems.)
The other question was about long term storage because I have been told by people that they get a chlorine gas smell in a closed closet. He said that the proper storage would be dark, cool and well ventilated. I asked about the results of storing it in a sealed container. He said that this would not be a good idea because you end up with a pressurized container of chlorine gas. You cannot stop the slow decomposition to chlorine gas. Their product has a 73% guaranteed available chlorine for one year from manufacture.