Water filters for outdoors: everything you need to know

Whether out trekking, on your bike or on a trip, sooner or later your water bottles will run dry. You could decide to save weight on drinking water, but exercise, especially during those warm summer months, can be thirsty work. We therefore recommend saving weight with an outdoor water filter. You can use it to treat water from streams and rivers when out and about. Water from wells is not usually classified as drinking water. In Switzerland at least, public wells in villages or towns must be adequately labelled if the water is not drinkable. It is a different story in the mountains or on private land, where no such labelling is required. This means that the water can also come from a stream. So you need to watch out when refilling your drinking bottle. In the ‘best-case scenario’, pathogens such as bacteria or viruses might only upset your stomach; in the ‘worst-case scenario’, pathogens can transmit life-threatening diseases. Here you will find an overview of mechanical and chemical water filters as well as filtering with UV light. There is a wide selection and different filters will be suitable depending on the activity and country or region. If you are unsure: Just drop by the store – we’ll be happy to advise you in person.

Mechanical outdoor water filters

There are different mechanical systems of drinking water filters. You might keep an eye out for the pore size. With a pore size of 0.2 microns (micrometres), they filter protozoa (single-celled organisms) and bacteria from the water, but the filter does not retain viruses. Water filters with a maximum pore size of 0.02 micrometres also retain viruses.

There are different systems to filter the water. Some work with pressure, while others require pumping. If you need to provide a lot of water at once, we recommend a model in which the water drips through without any external influence.

In some mechanical water filters, activated carbon is already integrated in the filter or there are suitable additional filter classes with activated carbon granules that can be added – for example, from Katadyn or LifeStraw. Activated carbon improves the taste of the water and binds many harmful substances dissolved in the water, such as agricultural fertilisers, chemicals and heavy metals. While activated carbon does not completely bind the harmful substances, it greatly reduces them.

Below you will find an overview of how different mechanical water filters work, along with their pros and cons.

Maintaining and cleaning water filters

Es ist wichtig, dass du den Wasserfilter sorgfältig reinigst. Nur so wird das verunreinigte Wasser It is important that you clean the water filter thoroughly. This is the only way to ensure that contaminated water can become drinkable. Follow the manufacturer’s instructions for cleaning and maintaining your outdoor water filter. As a general rule:

• Never clean the filter with soap or detergent. Depending on the model, you can detach the housing or individual parts and wash them in the dishwasher. However, you should only rinse the filter with clean water.

• If you can disassemble the filter into individual parts for cleaning, make sure they are well dried out before putting them back together. Residual water could encourage the proliferation of undesirable pathogens. Depending on the filter, the drying process can take several days. Exception: The Guardian model from MSR. If this filter dries out, water can no longer get through it and you have to buy a new filter.

• The residual water in mechanical water filters must not freeze under any circumstances. This is because water expands when it freezes and this can damage the filter. It may still look intact, but even tiny cracks are enough for bacteria and viruses to remain in the water. The Guardian water purifier from MSR is an exception to the rule. This is suitable for tours in winter, for example, when there is no snow to boil.

Chemical water treatment

You can use chlorine to treat contaminated water. This chemical is available in tablets, powders or drops. Important: The water must be clear. The tablets or drops do not filter out impurities. Also, do not use an aluminium or stainless steel container, as this could lead to unwanted reactions with the chemicals.

One advantage of this method is that tablets and powders are small and light. This means they can fit into almost any backpack. You can also use them alongside other filter methods to increase their effectiveness: For example, if your water filter only filters bacteria and protozoa, add chlorine to the filtered water. This works against potential viruses.

One disadvantage of this method is that chlorine takes at least half an hour to take effect. And up to three hours when used with cold water. This means you cannot drink the water straight away, but it can be kept for up to six months afterwards. However, it often has an aftertaste. Katadyn Antichlor gives the water a more neutral taste.

Water treatment with UV light

UV-C light kills bacteria, protozoa and viruses. You need clear water for this, as fine particles block the rays and reduce the effectiveness of this method. You might therefore need to filter it beforehand – a clean, tight-woven T-shirt as a filter or a coffee filter can be used in case of emergency.

The advantage of this method is that no taste is left behind from the UV light and the water is immediately drinkable. In addition, the devices are relatively small.

The disadvantage of this method is that the device is powered by batteries or a rechargeable battery. You should therefore always pack spare batteries or you will need electricity from time to time to charge the battery.

Which water filter would you recommend?

The type of water treatment you choose depends primarily on your specific location and the sources you can use to get your water.

If you are travelling in Northern and Central Europe, a mechanical filter with a pore size of 0.2 micrometres is usually sufficient. Viruses remain in the water, but pathogens such as hepatitis A or polio viruses are absent or extremely rare in these regions. If you want to err on the side of caution, you can also add a chlorine tablet to the filtered water.

When travelling to distant countries, make sure you are well informed about the types of pathogens found in these regions. This will help you to decide on the right water filter.

Which types of water are suitable for filtering?

You cannot actually find drinking water in nature. Exceptions include: Freshly collected rainwater and dew. You can never be sure which other types of water are actually drinkable. Fast-flowing water is usually cleaner than slow-flowing or stagnant water. But even then it is impossible to tell, for example, whether there is a dead animal in the water further up the river or the water is contaminated with animal droppings.

• Cool water tends to contain fewer germs than warm water.

• It is best to take the water from a fast-flowing stream - the further away from the bank, the better, as less sediment and pollution is deposited there. But be careful: these places are often difficult to access because fast-flowing water can undermine the bank.

• Civilisation and alpine farming influence the water quality. Above the pasture border and away from inhabited areas, the bacterial load in the water drops strongly.

A filter does not help with:

• Sea water

• Water from tailing ponds in mining

• Water from ponds or brooks, particularly where farms are nearby. No filter is capable of retaining all chemical impurities from agriculture or industry.

Filtering water without equipment

If your filter breaks while out and about and you do not have any tablets or any special water treatment utensils with you, there are other ways you can make water drinkable.