Planning | Water

Imagine being in the middle of the Sahara desert, Death Valley California, or any other hot and dry place. It is a desolate landscape, where the wind and arid climate evaporate the moisture out of your skin. What would be the one thing you would want out there that you probably aren’t going to find? How about a big glass of ice-cold water? Sure, here at home it’s easy enough to get; simply turn on the tap and it’s right there at your fingertips. What do you do when the power goes out or when a sewage line ruptures and bleeds into the city water supply? Do you really want to drink water that is infected with bacteria, viruses, or maybe even intestinal parasites? The next question to ask yourself is “Am I prepared to locate and purify water?”  if so then “What means and methods will work best for my family and myself?” In order to answer these questions, let us take a look at what we are trying to filter out of the water as well as the four major methods of water purification.

So How Dirty Is It Anyway?
So what’s in the water and how do you get rid of it? A quick scan on UNICEF or the Environmental Protection Agency’s respective websites will point out arsenicosis, cholera, fluorosis, HIV/AIDS, typhoid, and intestinal worms, along with several dozen other nasty diseases as the main culprits to look out for in your water supply (1, 2). While not something normally common in the United States, the United Nations’ water and hygiene development report of 2009 states that approximately 3.5 million people a year worldwide die from unclean water (3). So while typhoid may sound like something from the 19th and 20th century, and malaria as far away as Africa, the fact is, is that these type of aliments will pop up anywhere that bad hygiene conditions reach a critical point. In order to stay fit and healthy while drinking water of unknown quality in a disaster scenario, it is very important to take steps towards water treatment.

To purify water you must remove or kill all the micro-organisms in it and to do so there are several options available:

  • Boiling
  • Mechanical Purification
  • Chemical Treatment
  • Ultraviolet Light

Each method has pros and cons which will discuss here, but let’s start out with the oldest first.

Boiling Water
Modern scientific study has proven that the mere act of bringing water to a boil, not boiling for a certain length of time, will actually kill off the bacteria and viruses. The reason for this is simple really, water temperatures at or above 160° F (70° C) kill all pathogens within 30 minutes. If the water is at or above 185° F (85° C) this time is reduced to within a few minutes (10 to 12). So in the time it takes for the water to reach the 212*F boiling point (100° C) from 160° F, all pathogens will be killed. This is according to the Wilderness Medical Society, and is now considered a rule of thumb for water purification. To be extra safe, let the water continue at a rolling boil for roughly one minute, especially at higher altitudes where water boils at a lower temperature. However, there is a downside to this method. Boiling water requires a strong and consistent heat source and a lot of fuel, especially if you are going to be treating large quantities of water. That is something that should be taken into consideration before relying solely on this method for clean drinking water.

Mechanical Filtration
Now let us transition to mechanical filtration with its gravity and manual style filters. Gravity filtration is exactly what it sounds like. You pour unclean water into it and let the flow of gravity pull it through a cleansing media while manual filters involve using a pump to push the water through the filter element. Filter types vary greatly from charcoal and sand to a series of mesh screens and membranes, to the more modern multi-stage ceramic filters. As water runs through the filter, the filter stops the impurities from slipping through by trapping them inside. For this reason filters are rated by micron size, and you should pay very close attention to what that size is when you are looking at purchasing one. One micron is 1/1,000 of a millimeter and for reference; a human hair is roughly 90 microns in diameter. In order to remove parasitic eggs, bug larvae, as well as protozoa from the water, you will need a micron rating of 1 or less. In order to strip out microbiological contaminants (IE: bacteria) the filter(s) will need a micron size rating of less than 0.4.

Gravity filters allow for a large amount of water to be purified with a very minimal effort and next to no maintenance required. Most filters in this class will do roughly 1-2 gallons an hour per filter element. The good news is that most gravity systems are expandable, meaning you can add up to eight filter elements in larger units. In the case of the Crown Berkey, this upgrades the production rate to 26-gallons an hour, which is enough water for four adults and six children for a day, in one hour. The downside to gravity systems is their size and weight. The above mentioned Crown Berkey is nearly 30-inches tall and almost a foot in diameter when assembled. It is also made of 304 stainless steel. While smaller backpack-sized variants are made, they are still pretty heavy and probably not something you are going to want to hike around the woods with. As a side note, water bottle or inline filters such as the Sport Berkey fall into this category and are often just smaller versions of the manufactures’ main filter lines.

Meanwhile, pump filters require a much larger effort on the part of the user. The advantage of pump filters is that you can usually get water out of harder to reach places, like small puddles or natural springs in the mountains, places bottle and water containers just can’t fit into. Pumps tend to also move water at a much higher rate of speed relative to their size. Your average manual filter will produce a gallon of clean drinking water in roughly 4-5 minutes. They are also usually very light-weight, ranging from just under a pound to just over and rarely measure larger than 10-inches long. The down side is that you are manually pumping the filter which can make for a tiring and long process when you are doing large volumes of water. Couple this with a relatively short filter life of 200 to 300-gallons (in comparison to the possible 10,000-gallons of gravity units) and what we have are useful units when on the go, but not necessarily advantageous for a long-term “bug in” scenario.

Chemical Purification
Now let’s jump to chemical purification. The most common types of chemical purifiers are oxidizers and chlorine or iodine based solutions. They come under several brand names all with slightly different chemical compositions but all work in a similar fashion. This method is great for doing large and small volumes of water because it comes in small, light-weight pill and liquid forms (you can carry as much or as little as you think you will need). Chemical purification also has the benefit of not really requiring any work whatsoever on the part of the user. On the other hand, chemical purifiers will leave a residue in the water which can give the water a chemical taste, and also take several hours to work in some cases. Oxidizers are the fastest acting chemical water purification option and possess the lowest added taste while producing the least amount chemical residue in the water, but are usually more expensive than chlorine or iodine.

Iodine is more effective than chlorine, but deteriorates when exposed to sunlight and leaves behind an unpleasant taste. Iodine may not be suitable for people with certain types of thyroid conditions. The unpleasant taste of iodine can be countered by adding ascorbic acid (vitamin C) to the treated water, but this should only be added after waiting the recommended treatment time because it neutralizes the effectiveness of the iodine as well as the taste. There has been some concern about possible adverse effects from using iodine over prolonged periods, but medical studies including one where prisoners used iodine over a period of several years has not proven this to be the case. Liquid Tincture of Iodine sold in pharmacies is one possible source. Add several drops per quart of water mix thoroughly and allow it to sit for at least 20 minutes. For purifying on the move look for the more convenient iodine tablets sold specifically for water treatment while hiking.

Probably the least effective method of chemical purification is chlorine. Chlorine is somewhat unstable, adds some taste to the water, and leaves behind some chemical residue now associated with a small cancer risk. Household Liquid Bleach that contains 5.25% sodium hypochlorite can be used. Do not use scented, color-safe, or bleaches with added cleaners. Add about three to six drops of bleach per quart of water, mix thoroughly and allow the water to sit for approximately 20-minutes. This method is often combined with flocking which causes contaminants such as pollutants, heavy metals, parasites, cysts, and dirt to clump together so that they are easily filtered.  Aquamira is an example of a highly effective product using this method.

Ultraviolet Light
The last method we have to look at happens to be the newest method on the market. Ultraviolet radiation is capable of inactivating all types of bacteria and parasites. Additionally, ultraviolet radiation disinfects rapidly without the use of heat or chemical additives which may undesirably alter the composition of water. On the other side of the equation, UV light only works in clear water. If there is sediment or debris in the water this method is much less effective, so it is recommended that a pre-filter is used with this method. Something as simple as a t-shirt or coffee filter will remove a large quantity of the larger sediment. It should also be noted that ultraviolet radiological germination units are very expensive compared to other methods, this is even more so true when you look at units that are used for larger containers of water, as most portable set ups will only purify approximately a 1-liter bottle at a time. The reason is that the wave length of light needed to kill the bacteria does not actually travel a great distance inside of liquid; which is why the portable units actually need to be “stirred” in the water. In this manner the light is allowed access to all of the water in the container, thereby neutralizing the bacteria much more effectively.

In summary, each method has its advantages and disadvantages when compared to the other methods. The key is to find which method, or preferably methods, will work best for you and your family’s needs. Be it a pump filter or UV system for on the go and a larger gravity filter for at home, with a few containers of chemicals for back up, it is important to map out a plan that will suit you and your individual needs.

1.)    United Nations Development Programme (UNDP). (2006). Human Development Report 2006, Beyond Scarcity: Power, poverty and the global water crisis.

2.)    United Nations World Water Development Report. (2009). Water in a Changing World.   Estimated with data from: Numbers 4 and 12.

3.)    WHO/UNICEF Joint Monitoring Programme (JMP) for Water Supply and Sanitation. (2010). Progress on Sanitation and Drinking-Water, 2010 Update.

Baker, M.N. and Taras, Michael J. 1981. The Quest for Pure Water: A History of the Twentieth Century, Volume 1 and 2. Denver: AWWA.