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How to Make Water Safe to Drink

Updated: 3 days ago

For those of you that like to get off the beaten track it is impossible to carry enough water for an extended trip so finding and processing water is a vital part of staying alive and well. With so many products on the market and so many nasties to watch out for, this blog post deals with the vital task of making water safe to drink. This isn't just useful for hiking, this knowledge is useful for general travel too, even day hikes.

A small disclaimer, this post is not designed to be the font of all knowledge on water processing. There are a large number of sites and good books on the topic. This post is just to provide a basic introduction and some ideas for processing.

Germs In Water

Typically these categories cover the pathogens (germs) typically found in water that means it is unhealthy to drink. Depending upon circumstances & location you may or may not have to worry about some of these above.

Particulate Matter

Sometimes referred to as suspended matter is typically the large stuff you can see, it could be organic or non-organic, either way you don't want to drink it, it can unsettle your stomach and the last thing you need is diarrhoea.


Most bacteria in water come from contaminated faeces or urine from humans or animals. We should ideally remove the following bacteria from our water to make it safe to drink.

  • E coli (Escherichia coli), typically found in cattle faeces.

  • Typhoid Fever, is uncommon in the UK, typically most cases in the UK are from returning travellers. Common places to get Typhoid is India, Pakistan, Asia, Africa or South America. Found in infected human faeces.

  • Vibrio cholerae is the bacteria that causes Cholera, an infection of the intestine. This is typically not an issue in the UK apart from travellers returning home, but may be of concern if abroad, especially and Asia.

  • Campylobacter , the most common cause of food poisoning in the UK and probably one of the most common bacterial causes of diarrhoea. This is also found in animal faeces.

  • Salmonella, is another common bacteria infecting the intestinal tract and spread through human and animal faeces.


There are thousands of species of protozoa (parasites and cysts), but these are the most common ones we are interested in for making water safe to drink.

  • Giardia, typically around 5 microns in size are the parasite responsible for the intestinal illness known as giardiasis. These are typically found in infected human, dog faeces.

  • Cryptosporidium, typically 4-6 microns in size are are normally found in infected cattle faeces.


Viruses are difficult to filter from water due to their very small size, typically 0.004 to 1 micron in size.

  • Hepatitis A & E are diseases of the liver, again transmitted through face of another infected human.

Insecticides & Pesticides

These are typically only found in streams near agricultural land, but groundwater can be contaminated by excessive rainfall and irrigation.

Heavy Metals

These can be present in water, especially in land around mining operations and typically come from ground water where acid washes and other nasty techniques are used to wash ore.

Techniques to Make Water Safe to Drink

1. Pre Filtration. This involves using a filter of some kind to remove the larger potential nasties, the Particulate Matter. Typically the brown bag/millbank bag, however even a bandanna or sock could be used in an emergency to filter silt and larger particulates.

2. Boiling. Typically this technique is used after Pre Filtration, but if you are in an area where virus are an issue and your filter doesn't take care of them, then you can even boil filtered water.

3. Filtering. Typically filters remove particulate matter, bacteria, parasites and cysts, with the more expensive ones removing virus and even heavy metals and pesticides. It just depends on the brand and the cost, but typically the cheaper hiker/backpacking ones just doing particulate matter, bacteria, parasites and cysts. For most scenarios this is adequate.

4. Treatment. This involves typically some form of chlorine to sterilise the water. Most forms of chlorine treatment will kill the top 4. This treatment is normally done directly on alpine or clear spring or running water. If the water does have any suspended matter or doesn't appear clear then filtering before hand is advisable as chlorine treatments may not be 100% successful if matter is present. Also drinking suspended matter can upset your stomach. It is therefore important to make sure you filter water if it has suspended matter first before treating the water.

5. UV Treatment. Various sterilisation pens are available to treat water.These will typically kill the top 4 but obviously require batteries. Carrying batteries may present additional issues. Again if the water has suspended matter it is advisable to filter first in order to prevent any stomach upset.

What Gear Removes Which Germ From Your Water

The following matrix is a list of various products for each of the above methods indicating which group of pathogens they deal with.


Mic - Filter size in microns

PM - Particulate Matter

Bac - Bacteria

Pro - Protozoa (Parasites & Cysts)

Vir - Virus

IP - Insecticides & Pesticides

HM - Heavy Metals


Generally, it is down to you to research and consider the risks in the area you are hiking, travelling and formulate your own plan based on the possible risks, but there are some typical rules and generalisations I use:

  1. Use a Brown Bag to roughly filter and then boil, if you have an open fire or enough fuel for your stove its a great option and results in clean water, with the exception of insecticides, pesticides and heavy metals.

  2. If your water is clear, especially alpine water and there is little risk of insecticides, pesticides or heavy metals then a water treatment such as Aquamira is ideal, especially for hikers as its lightweight. It has no aftertaste, and the reaction just gives off oxygen.

  3. If the water has some sediment in it then you can use a filter instead (if viruses are not an issue) or use a combination of filter and water treatment.

  4. If you are visiting an area with extreme silt you may wish to take a Brown Bag and use it to filter the water first to stop the silt clogging up your main filter.

  5. If you are using stream water in heavily agricultural land or have any concerns about excessive insecticides, pesticides or heavy metals then consider the new Sawyer S filters.

What Do I Do?

My advice is never drink water without performing a suitable type of processing. It just isn't worth the risk. If it looks really clean I use Aquamira, if in any doubt or I see sediment, I filter using a MSR Trailshot and then treat with Aquamira. Even when just travelling I use a Water to Go bottle, getting an upset stomach when travelling is no fun either.

Most of the hiking filters are susceptible to freezing so sleep with your filter in cold weather if you need to. If you do leave it out in freezing weather, just throw it away, it is not worth the risk of illness for the cost of a replacement.

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