Water Filter
Care
A water filter only protects you while it is clean, undamaged and used the right way round. These are the habits that keep it working, and the signs that it is finished.
Read your own filter's leaflet first. Filters differ, and the maker's steps always beat a general guide. If you are ever unsure about the water, boil it.
What a Filter Does and Doesn't Do
A filter is a wall full of holes too small for most germs to fit through. What it stops depends on how small those holes are.
Most Filters
- Straws, squeeze filters, pumps and gravity bags all work by straining
- They stop parasites, and the finer ones stop bacteria too
- They also catch grit and mud, which is what clogs them
What Gets Through
- Viruses are too small for most portable filters
- So are salt, fuel and most chemicals
- Check what yours is rated for. Reverse osmosis units are the exception
When to Add a Second Step
- Flood water, and any water near people, stock or sewage
- Filter first, then disinfect with purification tablets
- Or bring it to a rolling boil for one minute
Before First Use
Ten minutes at home saves working it out beside a creek.
Set It Up
- 1 Read the leaflet. Note how many litres it is rated for and what it removes
- 2 Flush it with clean tap water until the water runs clear. A few dark specks at first are normal with carbon filters
- 3 Work out which end is dirty and which is clean
- 4 Practise filtering a litre in the kitchen
Dirty End, Clean End
- Water goes in one end and out the other, always the same way
- Mark the dirty-water bottle, bag or hose so nobody mixes them up
- Used the wrong way round, a filter pushes its trapped germs into your drink
In the Field
The cleaner the water going in, the longer the filter lasts.
Start With the Clearest Water
- Collect from clear, calm water, away from the muddy edge
- Muddy water: let it stand in a container until the mud settles, then pour off the top
- Strain it through a cloth first to keep leaves and grit out
Keep Dirty and Clean Apart
- The dirty-water container is only ever for dirty water
- Don't let the dirty hose or your wet hands touch the clean end
- Cap the clean end as soon as you finish
After Each Drink
- Straws: blow back through the mouthpiece to push the water out
- Shake out what is left
- Put the caps back on
Clean a Slow Filter
A slow filter is a clogged filter. Don't force it. Clean it.
Backflush
- 1 Fill the syringe or cleaning bottle with clean, filtered water
- 2 Fit it to the clean end of the filter
- 3 Push the water backwards through the filter, firmly
- 4 Repeat until the water coming out is clear and the flow is back
Straws
- Blow back through it sharply after every use
- Rinse the mouthpiece in clean water
- If it is still hard to draw through after that, it is near the end of its life
Scrubbable Elements
- Some pump filters have a ceramic element you can scrub
- Use the pad supplied, lightly, and rinse it in clean water
- Never scrub a filter that is not made for it
Backflush only with clean, treated water. No soap, no boiling water and no dishwasher unless your leaflet says so. Heat and detergent damage most filters.
Sanitise, Dry, Store
A damp filter left in a pack grows whatever it caught.
Sanitise
- Backflush it first
- Many makers then say to run a weak mix of plain, unscented household bleach and clean water through it
- The strength differs by filter, so use the amount in your leaflet
Dry
- Shake out as much water as you can
- Leave the caps off and let it air-dry out of direct sun
- Give it several days. The inside dries slowly
Store
- Cool, dry and out of the sun. Not a hot shed or car
- Somewhere it cannot be dropped or crushed
- Keep the syringe, hoses and leaflet with it
Never let a used filter freeze.
Water left inside expands as it freezes and cracks the filter from within. It still flows, so you cannot see the damage. If a wet filter has frozen, replace it. On cold nights keep it in your sleeping bag.
When to Replace It
Filters wear out. Know the signs before you rely on one.
Replace It When
- The flow stays slow after a proper clean
- It has filtered the number of litres it is rated for
- It froze while wet, or took a hard drop
- The housing is cracked, or a seal is missing
- A carbon stage stops removing taste and smell
Carry a Backup
- Purification tablets weigh almost nothing and cannot clog or crack
- Check the expiry date, and follow the wait time on the pack
- Boiling always works, if you have fuel and a pot
Water You Can Trust
Filter straws, pumps, gravity systems, tablets and storage.
More From the Survival Hub
This guide is general information only and is not health advice. Filters differ in what they remove, so always follow the instructions that came with yours. If your water authority issues a boil water notice, follow it. In a life-threatening emergency, call Triple Zero (000).