Water filtration by Rupert Brown

Doordat wij op diverse social media altijd weer de discussies en vragen terug zien komen betreft waterzuivering, hebben we besloten dit mooie artikel in deze blog te delen. Hier volgt een uitstekend artikel geschreven door onze vriend en collega Rupert Brown, hij is de man achter Browns Bushcraft en natuurlijk
The Brown filter bag. Het artikel is in het Engels geschreven, mocht er behoefte zijn naar een vertaling, laat dit dan weten!

Because we always see the discussions and questions about water purification returning on various social media, we have decided to share this very well written article by our friend and colleague Rupert Brown in this blog, he is the man behind Browns Bushcraft and of course
The Brown filter bag.


Water purification

Water is one of the most important things for human survival. Unfortunately, we take it very much for granted. However, when you have no water it then becomes the most important thing in your life.

Our bodies are made up of approximately 70% water. Every physical and chemical process in the body requires and uses water. For example, in muscle use, thinking, seeing, hearing and digestion.  All these processes use water in addition to what you will naturally lose through breathing, urinating and sweating. A small loss of 1-2% from your body will already start to have a negative effect on how your body functions. Keeping hydrated will help maintain physical and mental performance.

Under normal conditions the recommended minimum amount of water is 2 litres per day. That amount is only a guideline and will need to be increased significantly under certain conditions. It can vary due to the person’s size, fitness levels, illness, type of activity and type of environment. In very hot environments and with physical exertion the body can lose up to 2 litres per hour. Even in very cold environments your body will use a lot of water trying to stay warm.

Fast flowing river water may look clean but still needs to be made safe

If we are spending time in the wilderness and in remote locations, regardless of how brief that time may be, it is absolutely essential that you can locate and make water safe whilst on the go. Being able to find and process water will allow you to stay hydrated. It will also reduce the amount of weight you have to carry and enable you to stay for longer periods in the wild. You should always carry enough to last until your next source.

Whilst planning trips it should be incorporated into the route plan. Is there enough available water on your planned route?  Water happens to be heavy: 1 litre weighs 1 kilo. We should never resent this but, on the same hand, it would be foolish to try and carry enough for a 3-day hike.


Once you have found a suitable source of water you need to understand what potential contaminants are in the water to enable you to process it into safe drinking water. The five potential contaminants are:

1. Turbidity:

Turbid water is water that is dirty or cloudy. The contamination is visible in the form of mud, sand, silt organic matter such as leaves, twigs etc.

2. Viruses: 

Examples include Norovirus and Hepatitis A.  These are host specific, meaning you can only catch a virus from another human. Viruses are primarily spread when an uninfected and unvaccinated person ingests food or water that is contaminated with the faeces of an infected person. Viruses will be more common in areas of human habitation and can also be present in popular camp spots if people are not disposing of their human waste properly. Viruses can spread quickly within groups where poor hand washing facilitates transmission onto food and water.  Viruses will be less present in areas with little human traffic as well as countries with good sewerage and better hygiene practices. Viruses can spread quickly though if the sewerage system has been compromised, for example as a result of flooding or an earthquake.

3. Bacteria: 

Examples include E. coli, Leptospirosis and Cholera. They can be more widespread due to the fact they can spread through both human and animal waste. Bacteria can be spread through infected waste from both wild and domestic animals including farmed livestock.

4. Protozoa:


Cryptosporidium and Giardia can both be found in water everywhere in the world. Over the past twenty years they have been recognised as one of the most common causes of waterborne diseases. They can be carried in both human and animal waste.

Crypto and Giardia reproduce when the cysts (microscopic eggs) are ingested from contaminated food or water. The cysts have a very tough outer shell, they can survive outside a host in cold water for up to 2/3 months. They cannot tolerate freezing. The tough shell of the cysts can also protect them from short exposure to disinfecting treatments. In North America Giardia is commonly known as “Beaver fever”. This can be misleading, people can be mistaken for thinking that areas with no beavers will have no Giardia.



5. Chemicals:

Chemicals could be present in any water source as a result of farming, industry, mining, military, deliberate or accidental chemical spills. Chemicals are difficult to remove using the type of equipment bushcrafters and backpackers carry.

A microfilter type system may have an activated carbon filter which can help reduce chemicals. It is always better if possible, to try and find another source of water if you suspect it is heavily contaminated with chemicals.

Combine techniques

There isn’t one process that will effectively treat all these contaminants in one go, you will need to use a combination of 2 or more techniques to achieve safe drinking water. It is usually at this point that most people panic and either ignore the topic or buy an inappropriate piece of expensive kit that promises everything! There is a certain amount of confusion and misinformation surrounding making water safe, but there really needn’t be. It is relatively straightforward.

As a general rule to avoid any risk of illness I would treat all sources of natural water. It isn’t worth taking the chance not to. Coldness and clarity is not an indication that it is uncontaminated. In addition, travelling overseas to areas with poor sanitation, the fact the locals are drinking the water or that it comes from a tap is also not a safe indicator. Being ill through contaminated water or food is extremely unpleasant at any time. Vomiting and diarrhoea whilst out in the wild and away from flushing toilets, showers, fresh water and washing facilities is particularly bad. You may have a limited medical kit, be in a remote location away from medical support. If you don’t have access to a clean, safe supply for cleaning and, most importantly, to rehydrate then you will go into rapid decline due to extreme fluid loss through vomiting and diarrhoea.

Cholera, a water borne bacteria, can be fatal due to the violent liquid diarrhoea. Without rehydration an adult can die within 8 hrs. Water borne pathogens can be present in any source, whether in developed or undeveloped countries. Always check before travelling overseas to ensure you have the necessary vaccinations against water borne diseases. But crucially, don’t cut corners in treating water in the first place to reduce the risk of becoming ill.

Good discipline in the form of filtering and disinfecting is essential in order to reduce the risk of becoming ill. It can often be hard at the end of a long day trekking to find the energy and time to prepare some safe drinking water. Always try and adopt a routine once you have found a place to stop and ensure you allow time to prepare a sufficient quantity. Consider the following day, particularly if you are making an early start, will you have enough water prepared to carry to the next source?

Making water safe is a two-part process. Firstly, filtration and, secondly, disinfection. We only need to use filtration if the water is visibly dirty or turbid. Turbidity is a term used for water that contains floating debris such as mud, sand, silt, organic matter such as leaves, weed, twigs etc. It is first on the list of contaminants as it is the only contaminant that is visual – you can physically see it in the water.

We have to try and remove the turbidity for two reasons. Firstly, if sediment and debris is left it will reduce the effectiveness of any chemical disinfectant that is added. Viruses, bacteria and protozoa can latch onto any floating debris and hide amongst it. It then makes it hard for the chemicals to penetrate the debris and fully kill off any hidden pathogens. If you are using a UV light (Ultraviolet) system such as a Steripen, then the water must be filtered beforehand. If the visible debris is not removed the UV light cannot fully penetrate the water and deactivate all the pathogens.

Secondly, if the debris is not removed from the water and ingested it can upset your stomach and digestive system. We can filter to remove the floating debris by using a coarse water filter. This could be a piece of cloth, a bandana, an item of clothing such as a pair of trousers with knots in the bottom, paper coffee filters etc. Alternatively, you could use a purpose made canvas filter such as a Millbank bag or Brown bag.

Once your water has been coarse filtered it is by no means safe to drink at this point. It will have removed any floating contamination but not any potential pathogens. Pathogens are the viruses, bacteria, and protozoa. All water borne pathogens are microorganisms. This means they are only visible with a microscope or an electron microscope in the case of viruses. It is impossible to tell if water is free of pathogens by looking at it with the naked eye.

In order to disinfect the water, it must be treated and this can be achieved either with chemicals, boiling, microfiltration or UV light. When disinfecting water one of the key things to be aware of is “contact time”. Contact time is the amount of time microorganisms need to be exposed to your chosen disinfecting technique in order to either kill or deactivate them.


Chemicals can be in the form of tablets, liquid or powder. Chlorine, Chlorine dioxide and Iodine are the three most common types.

Chemicals are easy to use and take up little space and weight. Out of the three main types of chemical treatment, Chlorine dioxide is my preferred choice. Although more expensive, it has very little aftertaste, better results in killing protozoa and more effective over a range of PH.

As mentioned previously, protozoa cysts can be hard to kill due to the tough outer shell. If you are in an area with known protozoa then Chlorine dioxide is more effective in killing both Cryptosporidium and Giardia. Follow the individual instructions closely. Add the chemicals to clear filtered water then leave for the recommended contact time. Contact time is around 30mins for 1 tablet in 1 litre. In cold water, less than 10°C, to kill protozoa increase the contact time to two hours.

Once water has been chemically treated the chemicals do not offer long term residual protection. Within 48 hours the level of chemicals will have dropped to a point that they will not protect against re-infection. If stocking large volumes using jerry cans or tanks, perhaps for overland vehicle journeys or long-term fixed camps, you can add silver ion tablets to clean disinfected water to offer up to six months protection against re-infection.


Boiling water, if done correctly, is a very effective technique for disinfecting water as it will kill all microorganisms. It is combination of heat and exposure/contact time that kills of the pathogens.

Bring the filtered water to a rolling boil. A rolling boil is when the water has big bubbles and is really turning and churning in your pot.

When at a rolling boil it is a visual indicator that the temperature has reached 100°C. Once the water is at a rolling boil cover your pot, remove from the heat and allow to cool. Don’t leave the water boiling away as it is unnecessary and a waste of fuel. Any pathogens that are in the water are killed as the water is brought up to a rolling boil.


Once at 60-65°C it will start to deactivate some viruses. Bacteria will start to be killed and reduced at around 65°, protozoa at 70°. When up to temperature any pathogens will be killed within a minute of contact time. When the water is at a rolling boil it will have achieved both the temperature and exposure time needed to kill off any microorganisms. In addition, by covering and letting it cool, the water will remain above 70° for a while, thus extending contact time. Although boiling is an excellent method for disinfecting water, it may not always be practical. It takes time to make a fire and you may be in an area with a ban on open fires. Using a stove is practical but heavy on fuel.


Microfilters come in a number of forms ranging from hand pumps, in line, bags and straws.

They all have some form of microfilter built in which could be made from ceramic, paper or specialist fabric. The microfilter is fine enough that is able to filter and remove protozoa and bacteria but not viruses *. Some may have in addition activated carbon filters which can help remove chemicals, heavy metals and odours. In very turbid, dirty water it is advisable to pre-filter the water using a coarse filter. This will help reduce clogging and extend the working life of the microfilter. I would advise to add chemicals to the filtered water to remove any potential viruses.

Ultraviolet light: 

Ultraviolet, or UV, light is an invisible light. It is the shortwave germicidal UVC light that disrupts the DNA within viruses, bacteria and protozoa rendering them unable to reproduce and therefore, harmless. UV light is used in a lot of industrial applications for disinfecting large volumes of water such as in fish farms, breweries and treating domestic drinking supply.

For the backcountry traveller there is a small handheld UV light. The UV light element needs to be immersed in clear water and stirred for the recommended time. If turbid, coarse filtered first. You do need a wide neck bottle or deep enough billy pot to allow the UV light pen element to be submerged.  The advantages are it is quick, there are no chemicals and it will deactivate all pathogens. Disadvantages are the water has to be clear, it is electronic and battery powered, and there is always a risk it may fail.

In summary:

  • Treat all sources of water as being contaminated. This removes any risk.
  • Is the water turbid/visibly dirty? If yes then pass through coarse water filter such as bandana, clothing or Brown bag. Once filtered, disinfect either with chemicals, boiling, UV light, microfilter and chemicals.
  • If the water is visibly clear, simply disinfect.
  • In terms of equipment to carry for processing water. Firstly, a coarse water filter to filter dirty water. Secondly, a metal pot, cup or bottle to boil water. Thirdly, chemical disinfectant treatments. Adapt your water treatment technique depending on the situation. If you have time, and are able, then coarse filter and boil. If you are not able to boil then coarse filter and add chemicals.

The Brown filter bag

The Brown filter bag is a lightweight, compact, durable, virtually unbreakable water filter with an unlimited filtering capacity. It is both easy to use and carry and is available in two sizes, personal size with a 3-litre capacity and group size with a 20-litre capacity. Launched over four years ago, it is proving to be really successful and is being widely used throughout the UK and across the world. Brown Bags have been used in Australia, New Zealand, USA, Scandinavia and Europe.

I own and run Brown’s Bushcraft, a bushcraft school based in south west France. Along with most bushcrafters, I used Millbank bags for water filtration, and recommended these to students on my courses. The Millbank bag was used by the military worldwide for decades as a water filter but, when the army stopped using Millbank bags some years ago, they became more and more difficult to come by.

Simple and effective

This was my initial motivation for creating the Brown bag. Students would often come back to me saying they were finding it hard to find stocks of Millbank bags and asking if there was an alternative? The Millbank bag is such a simple, effective solution for filtering dirty water so I didn’t want to remove it from part of the watercraft teaching due to lack of stock. To meet the demand, I created the Brown bag as a replacement for the army Millbank bag.

Weight and weave

I tested many different weights and weaves of canvas but couldn’t find a canvas that performed as well as the original Millbank bags. As a result, I traced the original manufacturers of the Millbank bag canvas. The canvas is now woven to the same specification, only in a more subtle brown colour (rather than the original turquoise).

Once I had the correct canvas woven that was the first part of the project completed. I then needed to find a manufacturer for the bags. For me it was important that the bags were made within Europe. This would ensure regular contact and quality control. After trying a number of different manufacturers and rejecting the samples due to faults and inconsistency in the finished bags, I found the current manufacturers. They are UK based and the quality and finish on every bag is excellent.

The label


The next part was designing a label and to format clear instructions for the rear of the label. Finally the paracord was sourced and sent to another company to cut to length and crimp the brass ends onto the cord. A swing tag was designed and added to the bags with details of the bag and how to use it.

The whole process took nearly two years as I wanted to ensure the Brown bag was made to a high standard before being launched onto the market. I had to be confident people could rely on the Brown bag as a reliable means of filtering water with little risk of it failing or falling to pieces when needed.





London school of hygiene and tropical medicine

Once I had a completed bag, I contacted the London school of hygiene and tropical medicine to discuss running some experiments with the bag. The Brown bag is not designed to remove pathogens but we decided, out of interest, to run some experiments with the bags. A muddy solution, mixed with E. coli bacteria and microscopic fluorescent beads to mimic Cryptosporidium cysts, was passed through the Brown bags. The collected filtered liquid still had the E. coli bacteria present, but the microscopic beads were reduced by two thirds. So although still not safe for drinking the load for the sterilisation process was reduced. With all the research and attention to quality this now ensures a plentiful known source of new filter bags that perform as well as the army Millbank bags. With the both the canvas being woven in the UK as well as the production of the bags, the Brown bag is a 100% UK product.

Highly effective

The Brown bag is highly effective as a stand-alone water filter. The Brown bag can also be used in conjunction with a micro filter system as a pre-filter. Some micro filter systems are easily clogged if the solution has high levels of sediment. I often hear of people travelling in areas with high levels of water borne sediment and relying only on a combined purification and filter system then running into problems when the filter keeps blocking. By pre-filtering the water with a Brown bag you reduce the risk of the system clogging as well as extending the filtering life of the system.

Prior to using a Brown bag on your next trip, expedition or adventure it is essential that the new bag is broken in. The canvas is new so the fibres need to be opened and loosened up in order to allow the water to filter through.

How to break in your new bag

  1.  Start by saturating the bags. Ensure the bags are soaked thoroughly.
  2. Then be rough with them! Remember they are very durable and virtually unbreakable! Scrunch them up, massage and squeeze the bags. This will help to soften the canvas and open up the fibres.
  3. Repeat the process at least three or four times allowing the bag to dry in between.
  4. You can also put the bags in the washing machine to help break them in. Place them in a clean washing machine on a cold rinse cycle with NO detergent and NO fabric conditioner/softener. Always remove the paracord before placing in the machine.

Once your bag is broken in it is ready for use. With continued use the canvas will get softer.

How to use the Brown filter bag

Before you get started there are a few things to consider. You need a vessel to collect the filtered water. This could be a cooking pot, billy can or a bottle/canteen. It is generally easier to collect in a pot, particularly if it is very windy. It can be filtered into a bottle, but be aware of the fact that the wind can blow the bag around as well as the liquid flow from the base of the bag. If the bag and stream of water are blown around it results in most of the liquid missing the neck of the bottle.

Once you have a suitable vessel you will need to find something from which to hang the bag. For example, you can hang it from branches, pot hangers, tripods, or vehicles. Whilst filtering, the bag is hung from the supplied length of quality paracord, the para cord is 140cm long (55 inches) long and has metal crimped ends so could also be used as emergency cordage or an emergency shoelace. The instructions for using the bag are clearly listed on the label of the bag, so don’t worry about remembering them!

Instructions for using the Brown bag

  1. Soak the bag thoroughly before use by squeezing the bag under water.
  2. Fill the bag to the top with water to be filtered. It helps to have another cup or pot to scoop water into the bag if the source is not very deep. Note that if you’re using another vessel to scoop dirty water it will then be contaminated. Make sure it is sterilised before using again.
  3. Using your hanging point, hang the bag up. Look on the front of the bag and you will see a stitched diagonal line along the front. Before you put your collecting vessel under the bag allow the water to run to waste onto the ground until it reaches the level of the stitched line. Once the level has dropped to the line you can start collecting the water. In doing this it allows any debris or sediment that may have collected on the outside of the bag, whilst filling, to wash off rather than washing and dropping into your pot.
  4. The water will take at least five minutes to pass through the bag.  Use this time as part of your routine to prepare your camp in the meantime. Filtering can take longer if the water is very turbid, or the bag has not been fully broken in or soaked before use. In general the flow is steady but not fast, if the flow stops or is just dripping at the start of filtering it is worth checking the bag is fully saturated as well as checking it is not clogged with sediment from previous use. If the water has a lot of sediment the flow rate will decrease as the level drops in the bag. This is due to the sediment collecting at the lowest point in the bag.
  5. Once your water has been filtered it is still not safe to drink and must be purified/sterilised to remove any pathogens.
  6. Once you’re finished using the bag wash any mud or deposits from the outside of the bag. Then reach inside the bag and pull the bag inside out and clean any deposits from inside the bag. You can wash it out in water or dry the bag and then knock the build up of sediment out of the bag. Pay close attention to the lowest point in the bag as this is where the sediment builds up. This will help to maintain flow rates.
  7. After use it is essential to make sure the Brown bag is cleaned and thoroughly dried before storing.

* Update: There is one filter that i know of that does filter out 99.99% of the viruses, it works great i’ve tested it for the last two years and take it on every trip.. Check out by following the link  The GRAYL.

The Brown filter bag wordt gebruikt tijdens onze lessen en bij onze persoonlijke trips, en is binnenkort bij ons te koop!