Millbank Bag – Water Purification

millbank-bag1Modern purification pumps and gravity filter have become quite common and popular. Which is pretty obvious since water sources throughout the world have degraded in the last few decades. But these modern filters have drawbacks: their filter elements are usually made from fragile ceramic. They do not like to be exposed to shock or cold, as they might crack. Also the pumps, valves, O-rings, etc. can fail. That’s why a simple and reliable water purification system like the Millbank bag is still popular among some.
A millbank purification set is made up of a millbank bag and a form of chemical purification, usually iodine. It most also includes neutralising powder to neutralise the taste of iodine. A downside of the millbank is that it can not and will not remove chemical contamination, because it lacks a carbon element.
The principle is simple, chemicals like iodine or chlorine will usually stick on larger particles, so you will have fewer chemicals in the water to kill any bacteria, viruses or other biological threats, when many particles are present in the water. That’s why you use the millbank bag first to filter most of the particles and the larger organism out of the water. Allowing the chemicals that are added after the filtering process to do there job effectively. Also the millbank prevents you from having lots of sand and other things between you teeth. But filtering is slow and combined with the reaction time of the chemicals it will take even longer.


single person millbank bag

single person millbank bag


The millbank bag is a bag shaped like a sock. It’s made from very finely woven canvas, leaving very little space between the fibers. Because it’s only made from strong canvas fabric, it’s almost impossible to damage during normal use. Just don’t stick any sharp objects in to it, even if that happens you can repair the hole. It’s fully drop/shockproof and will not be as easily damaged by cold.
When using a millbank for the first time, wash it thoroughly to get the dust and other unpleasant thing out of the bag before use. A wash in the washing machine works great. To use the bag you have to soak it in water first. The soaking allows the fibbers to soak up water, making them larger. Thus making the space between the fibbers even smaller. When the bag has been soaked thoroughly, you scoop up water in side the bag and hang it on a tree branch or anything else. Just make sure it is strong enough to hold the bag.
Since the side of the bag is also contaminated with unfiltered water, you will have to wait a moment for the filter water to pass through the filter and flush the outside clean. There is usually marking on the bag that tells you to wait till the water has sunk below that level before collecting. When the water has sunk lower than the markings, put a form of collecting container underneath the bag. Group models usually lacks the markings because they have much more surface area and pressure to flush themselves clean and it takes a little more time to hang up. So by the time you get your cup under need it, it’s clean.
It’s harder to hang a group model up, because of a simple reason. A single person one has the capacity for approximate 2 litres, so you can hold it in one hand and use the other to hang and tie the string/rope to a branch. A group model can hold 5 gallons! (10 litres models are also available.) That’s a lot of weight you have to hang on a tree. Not something that you can do easily with just one pair of hands, but since it’s a group model you might as well ask the people in the group to help you. Also the bag is longer, so you have to hang it slightly higher. The height on the bag is suspended doesn’t really mater much. Just make sure it’s higher than the collection container and doesn’t drag over the ground.


size comparison - a single person millbank on top of a group millbank bag

size comparison - a single person millbank on top of a group millbank bag


The collected filtered water is now free of most particles. It can be safely be sterilized using chemicals, follow the instruction on the package. Make sure you do not have thyroid problems, allergies, aren’t pregnant and aren’t a child.
Washing the bag will prevent the filter from getting clogged. The bag should be stored dry, so let it air-dry after use when possible to prevent things from growing. The bag should be stored in a clean bag to prevent it from getting dirty.
Good points: ultra simple and reliable if used properly.
Bad points: it only filters particles, so it will NOT remove chemicals, bacteria and viruses, it is pretty slow and needs chemicals or boiling to complete purification.
Conclusion The millbank bag can be very useful for those travelling in places with reasonable clean water. It is very reliable, but it is slow and is a particle filter only. For most hikers and outdoorsman a modern filter will be a much better choice, due to there better filter capabilities and speed.


**if there are any points you would like to raise or any information you would like to add  regarding this article, please feel free to use the Comments box below.**

12 Responses to “Millbank Bag – Water Purification”

  • elon9669:

    Interested in making/sewing one. Do you know the material? If not where can I buy one to examine?

  • Tony:

    I’m sorry elon669 I have no idea what the material they make Millbank bags out of is called. If you want to buy one, they do come up on ebay every now and again.

  • peter:

    the mill bank bag can be made using artists canvas it is best to wash it first before you make it. i am in the process of making my own. plus a few other bits from the said canvas ………………….

  • Tony:

    Thanks for posting that tip Peter. I didn’t know that. Is there any chance of you taking some pictures of each stage when you make your Millbank bag and perhaps you could send us a tutorial that we could post here on Bushcraftstuff?

  • Hello, You made some good points there. I did a search on the topic with bing and found most people will agree with your blog.

  • Nigel:

    Hi, Just got myself a Millbank bag and tried it out. Did all the things as per the instructions but the water only came out from the bottom in slow drips. I don’t wish to appear dim ! but I thought it would trickle out. Have I been doing something wrong ? How do I improve the flow rate ?
    Please advise .

  • Tony:

    Hi Nigel,

    No you’re not doing anything dim. New Millbank bags often run very slowly to start. What might help to wear it in a bit and make the water flow through better is to chuck it in the washing machine. Don’t use any detergent though. If you’re not happy with doing this, just keep using the bag. It will improve as time goes on.

  • Excellent weblog, thanks for writing th is submit

  • Paul Uszak:

    I’ve used these so I thought I’d share my experiences. When I first received it, I tested it out in the garden. I filtered some green pond water that was loaded with algae. The water came out slowly as stated, but it came out crystal clear. I was amazed how effective it was. Also remember that it virtually takes no time as you just go and do something else whilst the water drips out. I then used it in the mountains of New Zealand filtering glacial river water. All the silt was removed and again the water was crystal clear.
    The only issue I’d raise is that of Cryptosporidium cysts. Having searched the interweb, I can’t find any information as to whether a Millbank bag can filter out crypto. That said, I think that you have to assume that it can’t and treat the water appropriately, which means iodine won’t do. So then you’re looking at boiling, UV or chlorine dioxide treatment. If you can live with that, then the bag is very good.

  • Andy Gray:

    I recently used these on a group trip in the Amazon. All our water for 30 people for two months was filtered though these and then purified with tablets. New Millbank bags water flow can be greatly improved by scrubbing the outside with a scrubbing brush, without jepodising the filtering ability. The more you use them, the better they get. Cost of a 2 pint one is about £10 ($7) in the UK – beats $100+ for a pump!

  • paul:

    hi guy,

    where i can buy millbank water filter bag. thanks

  • Tony:

    Hi Paul,

    I’ve noticed that there are a few sellers on ebay that quite often have Milbanks for sale. Obviously, make sure you purchase a new one. They tend to go for around £10 ($7).

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