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Thursday, January 8, 2015

Water Purification Basics, Part 2

When I started this series on filtration and other methods of treating water to make it fit to drink (the proper term is potable), I asked a series of questions on this blog about what a prepper might need from a water filter. In this post I will address the first two questions in more detail, and will cover the rest as I continue the comparison of treatment methods.

Those first two questions were "How clean do you need your water?" and "What is in the water that you need to remove?" For water to be considered potable, it must be free of any impurities or contaminates that would cause you harm when you drink it. That is the standard I use for how clean I need my water: will drinking it make me ill?

These questions are tightly linked due to the many sources of water available and their variations in toxicity. 
  1. Rainwater, snow melt, condensation, and water from deep wells are the least possibly contaminated sources that may be available. 
  2. Clear running water, like a mountain stream, is the next cleanest...
  3. ... followed by cloudy or dirty running water. 
  4. Shallow wells are prone to contamination from anything that hits the soil above the well, so I rank them below cloudy running water. 
  5. Stagnant or standing water is the most likely to be contaminated. 
Water that is supplied by a municipal (city or district) water treatment plant should be safe, but they are not infallible. There have been several “boil orders” issued in recent years for water that went through a municipal plant and wasn't fit to drink.

As a general rule of thumb, the closer you are to the origin of a source of water the better chance you have of it being clean. Rivers and streams collect contaminants as they flow toward the ocean. The poor folks that live downstream are going to have to work a lot harder to clean their water than the people upstream.

The EPA breaks contaminates down into six different categories that can be condensed into two --microorganisms and chemicals -- and that's how I deal with them. Most portable filters are rated for microorganism removal, with a few adding a carbon stage to remove some chemicals.

Microorganisms are treated either by filtering them out of the water or by killing them. Because they are considerably larger than chemical contaminates, they are easier to remove. I'm not going to list all of the possible bacteria, viruses, and parasites that can be transmitted through water since they are going to vary from location to location. There is one exception, however: Escherichia coli. E. coli is fairly easy to detect in a lab and is used as a standard for microbial contamination. Everyone has heard of E. coli, a form of bacteria that causes gastric (gut) illnesses when consumed. Most of the cases that make it into the news are from tainted, under-cooked meats or vegetables, but it is also often found in water. E. coli is a naturally occurring bacteria found in the digestive tract of mammals, and it survives outside the body quite easily. There is a threshold value to the amount of E. coli (and similar bacteria, all lumped into the phrase “coliform” or “fecal coliform”) that your body can handle; get too much, or the wrong type, and it will bring on nausea and diarrhea until/unless your body can kill off enough to get back into balance.

Chemicals are removed from water by breaking them down using heat or other chemicals, separating them out with a reverse osmosis membrane, or adsorbing them in a carbon filter. There are limits to how much of a chemical a body can tolerate, which vary by which chemical you're looking at. Some chemicals are dangerous in small amounts, with immediate consequences; others can be tolerated in larger doses over longer periods before they have an effect. Cyanide is immediately deadly in small doses, but lead can be ingested in for years before effects show. Heavy metals (lead, mercury, cadmium, etc.) are a widespread hazard that can have serious long-term effects on your health. Volatile Organic Compounds (VOC) are common solvents, pesticides, herbicides, and fuels that are sometimes found in water.

I need to make a definitive statement about filtration: 100% purity is not economically possible for preppers. There is no cheap way to get to zero contaminants, despite what some politicians and managers may say. (Chemically pure water is a pain to work with, anyway. It tends to dissolve metal pipes and containers.) 

With advances in technology, detection limits for most chemicals has gone from the parts per million (ppm) to the parts per billion (ppb) or even parts per trillion (ppt) range. To give some perspective, 1 ppb is being able to find one specific tire out of all of the cars registered in the USA, and 1 ppt is being able find one specific ¼ inch crack in a paved road stretching from Boston to LA.

1% = 10,000 ppm= 10,000,000 ppb=10,000,000,000 ppt. 

  • Since they can reproduce, removal of microorganisms at 99% is bad
  • 99.9% is still potentially dangerous.
  • 99.99% is bare minimum.
  • 99.999% will handle most contaminants.
  • 99.9999% is good.
  • 99.99999% is about the best you're going to find. No one thing is going to remove 100% of everything potentially present in water. You may see these percentages listed as “four nines” or “log four” (for 99.99%) removal.
Chemical removal will usually be listed as a percentage removed. If you don't see a log or percentage rating, you may see a micron rating for the filter element. Since most bacteria are around 0.2 to 2.0 microns in diameter, you'll want to look for a filter capable of 0.1 micron or better. Large organic molecules will range from 0.1 to 0.01 microns, while minerals and simple chemicals will range from 0.001 to 0.0001 microns. 

Top Names
I've been looking at various filtration systems that are on the market and here are some of the claims of removal efficiency. If I still worked in a lab, and I had the budget, I'd be tempted to test a few of these claims. Here are some of the common ones by brand:

Berkey is one of the big names in the water filter market, but they're not cheap. They insist that their units are water purifiers, and not just filters, which is fair since they use more than one type of treatment to purify water. They claim:
  • log 5 removal of viruses
  • log 9 removal of dangerous (pathogenic) bacteria
  • greater than 95% removal of heavy metals
  • VOC removal below detection limits

Sawyer makes a variety of things for backpackers and campers that also fit a prepper's needs. Their filters are a single-stage microfilter that traps everything larger than 0.10 micron and is rated only for microorganism removal:
  • log 7 removal of bacteria
  • log 6 removal of protozoa

One of the older names in water filters, Katadyn makes ceramic filters as well as reverse osmosis (RO) desalination units for a wide variety of uses. They are a bit shy about giving detailed specifications, but their ceramic filters are rated at 0.2 microns and their RO units are rated at 98.5% salt removal.

MSR makes a variety of camping gear as well and has bought the Sweetwater filter company. The Sweetwater uses a silica/carbon filter and is rated at 0.2 microns with some VOC and chemical removal by the carbon layer.

Please note that I am not endorsing any of these claims just yet. More info will follow, as next week I will delve into the physical methods used by the various types of filters and expand on the pros and cons of each. There's no magic involved in cleaning up your water before you use it, just a lot of technical jargon and marketing BS to dig through. I'll see what I can do to help make sense of some of it.

The Fine Print

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