Whilst water purification tablets can neutralise any water borne pathogens before drinking, if water is particularly silty or has solid matter in it then this can still cause irritation to the drinker from its physical effects, rather than its toxicity. To filter out these materials, Millbank filter bags have been issued since the Second World War and many soldiers routinely carry an example in their water bottle pouch. The British Army Millbank bag is a finely woven bag of green cotton, with a wide open top to allow water to be added, and it is sewn to a point at the bottom so that water passing through it comes off as a single stream and can be directed into a suitable container:
At the top corner of the bag is a brass eyelet that allows it to be hung up whilst water is percolating through it:
On the front is the date of manufacture, 1974, and an NSN number:
To use a Millbank filter bag Paul Kirtley on his survivalist website advises:
1. Soak the bag thoroughly by squeezing under water. SOAK the bag is what it means. It is not enough to wet it. This does not have to be in clean water. You must keep it submersed and massage the bag so that the fibres become wet through. This is important. Otherwise it can take hours for a couple of litres to run through the bag.
2. Fill the bag to the top with water to be filtered.
3. Hang up, and allow water to run to waste down to the level of the black line. Let water run out of – and off – the bag onto the ground (i.e. not into a container) until it is down to the line. This is why filling to the top (step 2) is important. By the time water gets down to the line, it will only be water from inside the bag that is dripping. You can then start to collect it (step 4 below).
4. Place water-bottle under bag, and fill. This should take about 5 minutes. Those who have used Millbanks will be laughing at this point. 5 minutes?! In my experience, they take a bit longer than this to fill a 1-litre bottle. Maybe 20 minutes. Those who have experienced the bags taking hours will undoubtedly not have soaked the bag enough in step 1. Spend 5-10 minutes soaking the bag in the first place. It’ll save you hours in the long run. If you are going to boil your water, you can drip it straight into a metal mug or pan. DO NOT drip water into your drinking bottle unless you are going to treat the water with a chemical sterilisation agent (step 6).
5. Afterwards, wash any mud off the bag, and replace in pocket. If you carry a small nailbrush as part of your hygiene and clothes washing kit, this is ideal for scrubbing a Millbank bag. If the water has been heavily laden with silt or similar, the inside of the bag will need cleaning from time to time, otherwise the passage of water through the bag slows significantly. Turn the bag inside out and scrub off any sediment.
6. Sterilise water in water-bottle using tablets from sterilising outfit. This obviously applies if you are using a chemical sterilisation agent (such as chlorine, iodine or chlorine dioxide). As mentioned in my notes to step 4, if you are not going to use chemicals to sterilise the water, don’t drip water into your drinking bottle as you have no way of then sterilising the inside of your bottle, even if you subsequently boil the water. Drip straight into the vessel you will use for boiling if you are sterilising the water this way.
N.B. If filling is slow, repeat soaking and squeezing under water. I’ve already mentioned how important the initial soaking is. Here the official instructions are reminding you how important it is. If the Millbank is taking ages to empty, it is more than likely it has not been soaked enough. Empty the water and SOAK it. Re-fill and start again. You’ll save time in the long-run.