By My DH PE (Civil Engineer)
As natural resources go, water is second only to air in importance to sustaining human life. But unlike air, the rarity of clean water in the areas of human population makes it a matter of concern for all of us. Since the target audience is preppers and survivalists, we’ll focus on methods that will be useful in emergency or survival type situations. I’ve clearly labeled sections so if you want to jump over the technical portions, it should be easy to do so.
We all talk about clean water. We all desire clean water. Some of us can even give a general definition. But when we treat water, we need to understand the criteria by which we judge clean water.
There are six categories of criteria that we must look at in determining water quality
Note that the first three are detectable by humans to a great degree and even better by most of our four legged friends. These are the tools nature has given us to determine if we should drink the water or not. But we have limits to our abilities to detect minute quantities of contaminants. So, we turn to technology to help us detect and filter out those we cannot detect. The bottom line is: as long as you can take enough stuff out of the water, you’ll have clean water to drink.
See the attached TBMED577 standards. This is the US Military standard for water quality. On page 90 and 91 you will find a list of criteria for non-potable and potable water respectively. From anecdotal data from over 20 bases in southern Afghanistan, with minor exceptions, the non-potable water is actually fit to drink as long as you kill the bugs. But in the US, there are higher standards than what humans are capable of taking. This is because of those minor exceptions. But if your source is reasonably clean, you should be fine with the non-potable standards as long as you take care of pathogens.
How many of you believe that boiling water will automatically make it fit to drink? Really? How would you feel about drinking raw sewage shortly after it has been boiled? Didn’t think so. Sorry to be so graphic. But I needed to drive a point home. While boiling will do a good job of killing pathogens, it will not take care of any other contaminants (solids, chemicals). These will effect, texture, smell, taste, as well as the overall fitness of the water for drinking or washing.
Distillation is often done through boiling. But it can also be done through room temperature methods. This will remove virtually everything from the water. There are several reasons not to use distillation as the method of water purification.
1) It does not remove any contaminants with a boiling point lower than water.
2) In the case of room temperature distillation, it does not remove contaminants with a vapor pressure greater than water. And this does not remove any airborne contaminants.
3) It removes essential minerals from the water causing it to deplete the body’s minerals and salts when ingested.
4) It is extremely costly and slow. Therefore, this should only be used for small-scale applications.
The modern world has invented all kinds of filters. Low tech filters include appropriate application of dirt (sand, silt, clay). Although it seems counter-intuitive to filter water by sending it through a filter made of dirt, it can be quite effective for a fairly clean water source. High tech solutions include membranes such as the famous Reverse Osmosis filters.
The premise is simple: water will go through and other stuff will get stuck in the filter. But it comes with several disadvantages. Take a look at the following numbers:
Viruses: 0.02 to 0.4 microns
Bacteria: 0.2 to 1 micron
RO: 0.00005 microns
Coffee filter: 20-40 microns
Tech filter: 10 microns (this is the filter paper that chemists use to remove precipitates from their solutions.)
Apart from RO and other similar filters, we don’t have very many filters that will filter out bacteria and viruses. Most automotive filters will be in the 5 micron range. Some go down to 1 micron. But the finer the openings, the more expensive it is.
The other consideration is that with any filter, you’ll need a method of cleaning the filter or you just have to replace it. With the smaller opening filters, replacement is more likely in lieu of cleaning. There is no way to clean an RO unit. You have to replace the membrane entirely.
There has been talk of using cotton cloth to filter water. This has been around the internet for a while describing a study done in various parts of the underdeveloped world. Such a study is not to be found. And from a technical standpoint, there is no reason to believe cotton has any ability to either kill pathogens or filter them out directly.
However, it can be used to remove particulates. Tightly wound cotton yarns or cloths can be used to filter out particulates down to 20 microns. And a great deal of bacteria (up to 80% by some estimates) can be removed by simply removing the particulates. 20% of the pathogens from a natural source is better than 100%. This is why they tell you to wash your hands—even without anti-bacterial soap. In fact, this is the simplest, most effective way to stop the spread of common diseases like the cold and flu.
The advantage of a cloth or yarn over other filters is that it can be washed clean after it has been clogged up.
There are only three methods I’m aware of for removing pathogens in water.
1) Chemically destroy them (antiseptics, chlorine, etc.)
2) Thermally destroy them (boil, burn, freeze, etc.)
3) Physically remove them (filtering, washing, etc.)
Most anti-bacterial soaps are great in the short term. But in the long term they are made of antiseptics that bacteria can evolve around. Eventually, they will become ineffective.
Chlorine (usually in the form of sodium hypochlorite) is a method of disinfection that is quite effective. The two great advantages of chlorine are that 1) bacteria and viruses cannot develop tolerance or immunities to it, and 2) if left open overnight, it will evaporate out of the water and will have no lasting effects in the water.
Vinegar is also an effective disinfector. This has long been an old wives tale. But Better Homes and Gardens did a laboratory study to determine that regular household vinegar is as effective as chlorine in disinfection. Unfortunately, it is difficult to remove from water and is therefore not a practical method in the disinfection of water.
A recent development at the University of Illinois at Urbana-Champagne has created a cloth made of titanium-oxide doped in nitrogen and treated with palladium. This cloth reacts with water creating a hydroxyl radical (the neutral form of the hydroxide ion regularly found in water). Hydroxyl radicals are extremely toxic to any life-form. Thankfully, these radicals have a half-life in the nano-second range.
Creating these radicals requires energy. The cloth absorbs energy from visible light and uses it to create the hydroxyl radicals. Here are the interesting facts.
1) Most raw sewage will have an e-coli count of 3,000 to 500,000 per liter.
2) They tested their fabric with a 10,000,000 count per liter.
3) It removed anywhere from 80% to 99% of the e-coli with a 25 second exposure.
4) It only requires exposure to visible light at about 2% the intensity of sunlight at sea level for a few minutes per 24 hour period to charge it.
5) After the active zone, the radicals dissipate quite quickly, leaving no lasting toxic effects.
6) These tests were done with 1g of fabric per liter of water.
I have asked the following two questions and am awaiting a response:
1) What was the source of the variation in disinfection?
2) How are you able to ensure contact between the radicals and the pathogens with only 0.022% of the volume occupied by this fabric?
This material has yet to be commercially available.
APPENDIX I: WASTE WATER TREATMENT PLANTS
The most common method of purifying water in the US is via the waste water treatment plant. Treatment plants take raw sewage from a municipality and treat it to become potable again. It may be difficult to put our minds around the idea that we’re drinking former sewage. But I assure you it really is pretty safe.
The first step is to screen the water through a series of smaller and smaller screens. The first one is a grate of about 2’ squares (depending on the city). The smallest one is about as big as a window screen. Within the screening process is a bunch of grinder pumps and traps to break down and catch debris. Periodically, the screens and traps will need cleaning or replacing. At this point we’re ready to move to secondary treatment.
High quantities of oxygen are introduced to the water causing bacteria to become highly active. This causes the bacteria to digest all the organics in the water and break it down to less hazardous by-products.
Then we move on to the settling tanks. This uses gravity to separate water from sludge and scum. Scum is lighter than water. Sludge is heavier than water. (So if you call a civil engineer “scum”, your actually saying he has floated to the top. So scum is a compliment). This is necessarily a slow process because so many particles are very close to the density of water.
The final process is chemical treatment. Here we use various chemicals to kill germs, neutralize chemicals, precipitate out solids, etc. Once through this, the water is cleaner than virtually any stream or river in the world.
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