Even in ‘pristine’ New Zealand, microscopic bacteria and viruses can be lurking in streams and hut water tanks. A water filter or purifier offers on-the-go peace of mind no matter where you drink from.

Water-borne hazards
True, New Zealand backcountry streams are reasonably healthy but even so there is a small risk that water-borne illnesses like giardia, campylobacter, salmonella and E. coli can be picked up. The risk in urban environments increases after a disaster like an earthquake or when travelling to developing nations, where viruses and bacteria pervade waterways. Hut water should always be boiled or filtered/purified.

Filters
Filters are the first line of defence against larger-than-a-virus protozoa and cryptosporidia such as Giardia Lamblia and parvum. Filters remove sediment and organisms down to 0.4-0.1 microns.

Purifiers
Purifiers kill the much smaller viral and bacterial organisms. UV light is the most common and effective form of purification. It is important to follow instructions preciely to ensure the purification process is adequate.

The full system
Some systems use both a filter and purifier. The filter removes organisms down to 0.2 or 0.1 micron and the purifier deals with anything smaller. Unless the removal of organisms is at least 99.9%, there is a risk of infection.

Flow rates
The usual flow (or purification) rate is one to two litres per minute. It’s important to keep filters clean and free of sediment to ensure the flow rate remains high.

Where to filter
Always check – if possible – what’s in the water upstream to avoid contamination. Giardia slowly sinks, so draw your water where the flow is slow moving, away from the bank. Avoid muddy water as it can contain bacteria stirred up from the streambed and will also clog filters.

Cleaning
To ensure the long life of your filter, clean it regularly. This is usually done by rinsing and can be accomplished in the field as well as at home.

MSR Guardian Purifier $699.99
Military-grade, pump-action purifier with hollow fibre filter to treat filthy water and remove viruses, bacteria,
protozoa and particulate. Self-cleaning, impact resistant, withstands freezing. For use in developing nations and popular wilderness areas. Removes 99.9999% of bacteria, 99.99% of rotavirus and poliovirus, and 99.9% of giardia and cryptosporidium cysts Flow rate 2.5-litre/min Cartridge life 10,000+ litres Weight 490g.

MSR MiniWorks EX $229.99
Easy-to-maintain microfilter, removes bacteria, protozoa and unpleasant tastes and odours caused by organic compounds. Field maintainable. Removes 99.9999% of bacteria, 99.99% of rotavirus and poliovirus, and 99.9% of giardia and cryptosporidium cysts. Flow rate 1-litre/min Cartridge life 2000+ litres Weight 456g.

SteriPEN Adventurer Opti $239.95
Compact handheld water purifier using ultraviolet light to kill up to 99.9999% of all waterborne bacteria and 99.99% of all viruses. Insert batteries, push the on button and insert it into your water container. Uses two CR123A batteries. Purifier life 8000-litres Output 1-litre/90sec Weight 110g.

SteriPEN Classic 3 $189.95
Patented handheld water purifier uses ultraviolet light to kill up to 99.9999% of all waterborne bacteria and 99.99% of all viruses. Pre filter included. Takes four AA batteries. Purifier life 8000-litres Output 1-litre/90sec Weight 225g.

Aqua-Straw $39.99
Two-layer filtration, filters to 0.01 micron, removes up to 99.9% of waterborne bacteria and protozoa, includes extension pipe and a threaded bottom compatible with many drink bottles, BPA-free. Filter life 1500-litres Weight 100g.

MSR TrailShot MicroFilter $129.99
Drink directly from the source or refill drink bottles, quick-deploy design, squeezing action pumps water through filter. Removes 99.9999% of bacteria, 99.99% of rotavirus and poliovirus, and 99.9% of giardia and cryptosporidium cysts. Flow rate 1-litre+/min Cartridge life 2000-litres Weight 153g.