We all need water to stay alive. Not just any water - it must be free from pathogens, poisons and ideally be palettable too. Sadly even the cleanest looking streams dont always promise all three of these and to make a mistake can range from unpleasant to fatal. There are a wide range of water treatment systems available on the market with costs and performance varying almost as widely, so which one to choose ? We'll try to take some of the mystery out of this important subject:
Broadly speaking there are two types of water - safe and not-safe. If you are not 100% certain the water is safe then you are wise to assume it unsafe and take appropriate precautions. Simply taking sufficient safe water with you resolves the issue entirely, but this may be impractical on longer trips and does not take into account emergency situations that may arise. If you do need to replenish from a source the integrity of which is uncertain, you will need some kind of water treatment facility with you.
To convert unsafe water to potable there are three types of treatment systems: mechanical (filtration) , chemical (neutralisation and sterilisation) and a combination of these (hybrid).
1. Mechanical Water Filtration
At its most basic, filtration removes particles and even some discolouration and odour from water without adding anything that wasn't there before. Filters work by passing the fluid though very small holes in a physical medium which traps unwanted particles and, if it is fine enough, even microscopic creatures; bacteria and viruses. The finer the filter the better the result but it also takes more energy to push water though ultra-fine filters and they can quickly clog if used with water with high levels of contamination. To counter this the finest filters tend to need to have larger surfance areas to allow a reasonable flow rate and lifetime which usually translates into higher purchase and running costs too.
There are two basic types of filters used in mechanical filters:
1.1 Membranes which have incredibly small and very thin atomic mesh-like structures which allow water molecules through but prevent almost any complex molecule which is larger from passing though, which includes most poisons, disssolved pollutants and microbiological pathogens.These are the most sophisticated filters and suitable for use almost anywhere in the world. Expensive and bulky, these systems have very high performance and are suitable for regular use in harsh environments - but make sure you have spares with you in case the membrane gets damaged or needs replacing.
1.2 Ceramic or activated Carbon (charcoal) filters which are naturally porous substances with many many fine and tortuous routes/channels through which the water is passed. Most (but not all) impurities and microorganisms are trapped by the filter as the water passes through these tiny channels. Most products in this category are fairly low cost and have high flow rates but can let the smaller pathogenths though and usually should be replaced if the filter medium is left to dry out. Typically these are lightweight and inexpensive so are great for emergency use.
2. Chemical Water Purification
Again there are two basic systems: Additive and Reactive. Both require an accurate measurement of the volume of water to be treated and some minimum amount of time before the treatment is complete so that the water is rendered nominally safe to use.
2.1 The additive chemical purification systems rely on adding a reagent which will kill microorganisms much like adding a disinfectant. At the correct dose and after the appropriate treatment time, the result is water which contains both the deactivated organisms and usually some traces of the chemical used although relatively harmless. Since no filtratiuon takes place, suspended matter is usually still present ( although heavier particles may have settled out a little) and there is rarely if any deactivation of poisions or non-biological threats. For the majority of clean upland water sources this is usually perfectly fine but is not sufficiently aggressive for use in heavily polluted regions.
2.2 Reactive chemical systems use external disruptors that disable the microorganisms but do not add anything additional to the water itself. The most commonly available systems utilise Ultra-violet (UV) light which kills/disininfects microorganisms exposed to it for the appropriate length of time and at a sufficiently high intensity. Since these systems are almost invariably electrical and portable, the quality and charge contained by the battery is imperative to ensure the correct dose is applied. Also, the size and shape of the container is extremely important to ensure adequate dose reaches the entire sample to be treated. In heavily contaminated water, UV light can be prevented from reaching the entire sample by the suspended matter itself so this is not a good solution for heavily soiled water. Irradiation by and high levels of magnetic flux can also be used against certain impurities but these systems are impractical and inadequate for mobile solutions.
3. Hybrid water Filtration/Purification
It should be noted that there are imperfections in ALL of the available water treatment solutions mentioned so far so some companies have developed hybrid systems to mitigate the weaknesses of each solution. These consist of multiple filtration and purification 'stages' that successively present cleaner water to the next stage and hence provide longer useful lifetimes and lower concentrations of chemicals / UV to be used. Even these are usually not sufficient to rid the worst affected water of all potentially harmful substances.
The Real World ... or 'how to stay alive'
Would YOU drink dirty or untreated water if you had no access to clean water?... regardless of what you may think you would do in these circumstances, survival experiences and third world poverty shows us that mankind will DEFINITELY drink filthy water rather than to certainly die by slow and painful dehydration. Dont think for one second that your 'civilised' instincts will supercede the primal requirement to sate your thirst and while extreme survival skill such as drinking your own urine may save your life, personally, I think I would much rather start each journey with some clean water and a water filter to refill with.
Remember even very low levels of dehydration from around 2% (by bodyweight) causes noticable loss of performance, impared judgement, increased reaction times, poorer concentratration and decision making, thicker blood with a raised heart rate to compensate, reduced sweating leading to overheating and if left to continue can lead to collapse and death.
One final practical note - with all treatment systems it is strongly advisable to have two water containers - one for untreated and one for treated/clean water which avoids cross contamination. If you use collapsible bladders this need not add much weight or bulk to your pack and means you can carry a lot more water than you can treat in one go, which is also particularly helpful when sources of water are scarce.
