Last week we looked at some natural methods of purifying water. However, sometime we don’t have the resources or time to apply these and sometime the water we are forced to drink is so much akin to the toxic urine from Satan’s own bladder that only technology can make it safe.
As with all things there are compromises with water filters. Be it cost, weight, bulk, effectiveness or speed. There are a number of specific manufactures and models so I’ll try and keep this general but will include links to examples of each.
Particulate – Not necessarily toxic but particulate, like mud, sand, dead beetles and random, suspicious lumps are not what you want to be drinking.
Protazoa – These are single-cell parasites and the group contains Giardia and Cryptosporidium, two of the most feared Gastro-Intestinal (GI) infections. Some pathogens can only be eliminated by more advanced filters
Bacteria – Much larger than viruses so relatively easy to filter. This group includes E.coli, a common cause of GI problems.
Virus – Smaller than bacteria, and therefore more difficult to filter, this group includes Hepatitis and Rotovirus
Chemicals – Chemical pollutant are wide ranging and are more common in urban, industrial or certain agriculture areas.
Your filter need not deal with all these. Research where you’ll use it, what the local risks are and get what you need.
Weight/Bulk: Depending on whether you are trekking, paddling or using a vehicle the weight and bulk of your filter will be more or less important. However, it’s usually a compromise between filtration rate and size.
Cost: The more effective, lightweight and the greater its filter rate then the more it costs. Think about what you really need so you’re not spending your hard earned cash needlessly.
Filtration rate: Filters can only filter so many litres per minute. The smaller the filter and/or the more toxins they filter the slower they are. So you need to consider how much clean water you need (group size, exertion, local conditions, cooking methods) and how much time per day you’re willing to dedicate to the job.
Gravity: These systems use gravity to force the water to flow through the filter. They can be slower but can be set up and left while you busy yourself with other things, so handy at a camp. The type of filter will effect what it kills. https://www.platy.com/ie/filtration/gravityworks-4-0l-filter
Pump: The most common type. Hand-pumping forces the water through the filter. Faster than gravity but means you have to stop and dedicate time to this task. Like the gravity fed filter the type of filter will effect what it kills.
Straw/Bottle: These use your sucking action to draw the water up through the filter. The straws are very small and lightweight but you can only use them at the water source. Unless you want to be spitting out mouthfuls of clean water into a bottle you can’t take it with you.
Example – http://lifestraw.com
You can get sports-bottles that you fill with the polluted water and then drink on the hoof. I use these a lot, even in urban areas where I can fill from public toilets or hotels. It saves buying bottled water and producing even more plastic waste.
UV: These use electricity (so you’ll need batteries) to pulse UV light into the water to kill Protozoa, Bacteria and Viruses. However, to work effectively the water has to be reasonably clear so a simply filter to take out particulate is also necessary.
Example – https://www.steripen.com
Chemical: These are chemical drops or tablets usually made of chlorine or iodine. They kill Protozoa, Bacteria and Viruses but long-term use (i.e. constant use over many weeks) of things like iodine may cause health issues. They also may need a few hours to work.
Think about where you’ll mostly be using your filter. Something that kills everything, filter 100 litres/minute but costs a bomb and weighs a ton is a bit pointless for solo trips in Scotland. I used to have a hand pump which was fine for most of Europe. If I used it in places where the water was more contaminants I’d pump-filter it then add a chemical, so perhaps a combination of two types will give you maximum flexibility for the right price.