Water filtering and filters
Water filtering and filter
Water, water everywhere…
Many of us have heard the survival rules of 3s.
You can survive:
If you are like me, and think with your stomach then you might prioritise food, but this shouldn’t be the case. Shelter is already a big focus of the survival community and hopefully oxygen will be readily available, so I want to talk about water.
When outdoors, it’s easy to become dehydrated without realising it. Dehydration can affect your concentration, mood, strength and stamina, so you should drink at least 2 litres of water a day and more if you’re being active. Weighing in at 1kg per litre it adds a lot to the load on your back, so if you don’t have access to clean water for extended periods you will need to find some from a natural water source. How do you know that there isn’t a dead animal, sewage or other bacteria contaminating your water? You don’t! If you get it wrong, your stomach will pretty much jettison everything in it. You could quickly end up more dehydrated or worse. You can end up in a dangerous position.
Water purification
Making water safe to drink typically requires 2 processes:
- Debris need to be removed.
- bacteria in the water need to be neutralised/removed.
Most water purification processes do this in one of several ways.
- Killing the bacteria via boiling
- Killing the bacteria with chemicals
- Removing the bacteria and other organic materials via filtration
It’s worth mentioning that most standard water purification methods will not make chemical contamination or salt water safe to drink. Carbon filters will help in some situations but usually distillation[v] or reverse-osmosis[vi] should be used.
Filtration – It’s all about size
To remove bacteria and other contaminants using filtration you need a filter with holes smaller than the organic matter. Think of it like a very narrow road bridge, if your car is wider than the bridge it can get through! If you’re a geek like me and want to know exactly how big these particles are, there’s a list here:
http://www.portablewaterfilters.org/water-filter-guide/particle-contaminant-size-chart-microns/
If we were to compare how a 0.1 micron (100nm) and a 0.015 micron (15nm) filter would deal with a 0.08 micron (80nm) wide virus it would look something like this:
Simply put, the smaller the filter hole, the more material it blocks.
Common water purification systems
Millbank Bag plus sterilisation tablets
Dry weight: 50g
Size: 40 x 18 cm
UKSN price: £10.99 - BUY HERE at P1AN
How?
Millbank Bags are used to pre-filter general debris, however, the weave is not tight enough to filter bacteria, so you need to kill them chemically with sterilisation tablets or by boiling the water.
Hang the bag from a branch and fill it to the brim. Once it has dropped to the level of the marked line you can start collecting the water that is dripping through the bag. Then either put in 1 sterilisation tablet per litre of water or boil for at least 3 minutes.
Pros
- Lightweight
- Compact
- Cheap (although there is an ongoing cost buying replacement tablets, unless you boil the water)
- Doesn’t wear out
- No complex maintenance or storage
Cons
- Time: It can’t be done on the move. You have to wait for the water to pass through the bag. Sterilisation tablets then require half an hour to work. Boiling water also takes time as a fire source needs to be set up.
- Sterilisation can add an unpleasant taste.
- Sterilisation tablets wont always kill all the bacteria
- Boiling water uses up fuel.
Lifestraw
Dry weight: 57g
Size: 22.5 x 2.5 cm
Price: £19.13 - Amazon
How?
The Lifestraw uses filtration to purify water. With 0.2 micron (200nm) filter holes if will stop bacteria but unfortunately wont stop most viruses or cysts. It will purify up to 1,000 litres of water, 500 days worth!
As the name suggests you use it like a straw, so it’s very easy to use, just put it in water and suck. You can also fill up a bottle with dirty water and drink from it using the straw.
Pros
- Simple
- Lightweight
- Small
- No other equipment needed
- Filters most bacteria and parasites
- Easy to use
- Cheap
Cons
- Doesn’t filter viruses
- At 0.2 micron (200nm) it wont remove as many contaminants as other filters
- Doesn’t come with water storage
- Compared to other systems 1,000 litres is fairly low.
Sawyer mini
Dry weight: 57/65g (with/without accessories)
Size: 13.5 x 3 cm
Price: £23.95 - Amazon
How?
The Sawyer Mini has filter holes that are 0.1 microns (100nm) wide. These can stop the bacteria but as with the Lifestraw, very few of the viruses or cysts. It will filter up to 450,000 litres, providing an incredible 225,000 days of clean water!
To use you can either put it in dirty water and suck, or attach it to either the included pouch or tubing. It’s not easy to fill the pouch by immersing it in water (I suggest inflating it first) but the filter will also screw on to the top of most standard soft drinks bottles. If you want to upgrade to the bottle version of the Sawyer, this is sold by P1AN and can be bought HERE.
Pros
- Filters most bacteria and parasites
- Lightweight
- Fairly small (when extras are carried)
- Filters up to 450,000 litres!
- Can screw on to most standard drinks bottles
- Can be gravity fed
- Can be used inline as part of a bladder hydration system
- Relatively cheap
Cons
- Doesn’t filter viruses
Lifesaver bottle
Dry weight: 1.06kg
Size: 13 x 19 x 21 cm
Price: From £40 - P1AN
How?
With a filter size of 0.015 microns (15nm) this system filters bacteria AND almost all viruses, making it a market leader. Lifesaver have two versions of the Lifesaver bottle, the 4000UF and 6000UF. They claim that each can filter up to 4,000 and 6,000 litres respectively, that’s 2,000 or 3,000 days.
To filter water just unscrew the bottom, fill the bottle with water, and pump the handle to force the water through the filter and out of the mouthpiece. As the filter is built in to the bottle it means you have a container for carrying water around in too.
Once used for the first time the filter needs to be kept wet, so simply store with at least 3cm of water in it, and change the water every few months to stop it stagnating. UKSN Lifesaver bottles come primed and tested so water needs to be kept in them at all times.
The bottle comes with a carry strap but fits nicely in many rucksack side pockets. All parts are replaceable and interchangeable.
Pros
- Filters most bacteria and parasites
- The only filter here that removes viruses too
- Stores water so you can filter on the move
Cons
- Large
- Relatively heavy
- Expensive at RRP
Round up
Each system has its advantages and disadvantages. Personally I carry at least 3 methods of obtaining clean water with me in my rucksack. Which ones will depend on where I am, whether I am on the move, and what water source is available in the area.
Method |
Weight |
Size (cm) |
Filter size (microns/nm) |
Litres produced |
Eliminates bacteria |
Eliminates viruses |
Speed |
Cost |
Millbank bag plus tablets |
50g |
40 x 18 |
Large |
Depending on amount of sterilisation tablets available |
Yes* |
Yes* |
Slow |
£ |
Lifestraw |
57g |
22.5x2.5 |
0.2/200nm |
1,000 |
Yes |
No |
Fast |
£ |
Sawyer Mini |
57/65g |
13.5 x 3 |
0.1/100nm |
450,000 |
Yes |
No |
Fast |
£ |
Lifesaver bottle |
1.06kg |
13x19x21 |
0.015/15nm |
4,000/6,000 |
Yes |
Yes |
Very fast |
£ |
* When used with sterilisation tablets or boiling
Sources:
[i] http://www.backcountrychronicles.com/wilderness-survival-rules-of-3/
[ii] http://www.huffingtonpost.co.uk/2012/02/20/mild-dehydration-causes-a_n_1288964.html
[iii] http://www.nhs.uk/Conditions/Dehydration/Pages/Symptoms.aspx
[iv] http://www.naturalhydrationcouncil.org.uk/hydration-facts/
and
http://www.huffingtonpost.com/2013/06/27/dehydration-myths_n_3498380.html
[v] http://thesurvivaldoctor.com/2014/01/20/how-to-remove-chemicals-from-drinking-water/
[vi] http://npic.orst.edu/envir/dwater.html
[vii] https://www.iconlifesaver.com/product/lifesaver-bottle-4000uf
[viii] https://www.cdc.gov/healthywater/drinking/travel/backcountry_water_treatment.html