Drinking water on the mountain: Filling your bottle at the spring - good or bad idea?

Has anyone ever been to the Canadian Chilcotins? A wild mountainous region in British Columbia that can only be reached from Vancouver by seaplane. It takes several days to get back to civilisation on trails. Great adventure land for mountain bikers, with lakes, forests, mountain passes, river crossings, bear encounters and not a soul around. What reason could there possibly be here not to simply fill up your bottle in the crystal-clear bubbling stream?

"Don't even think about it!" our Canadian guide almost got angry when he caught us doing this. "You never know if there might be a dead animal in the water further up!" Oh, it's scattered in the water, isn't it? Not a chance. It almost seemed as if the man had already had a bad experience himself.

Huts also draw their water from springs

In May 2024, guests at the Rotwandhaus in the Bavarian Mangfallgebirge mountains certainly had a bad experience. At the time, 21 mountaineers spent the night in the popular hut, which is located just under 1700 metres above Lake Spitzingsee and draws its water from a mountain spring just below. In the end, the mountain rescue team had to arrive and take all the hut guests down to the valley with severe gastrointestinal complaints, eleven of them even to hospital.

Coli bacteria as well as noroviruses and rotaviruses were identified as the cause in the hut's tap water. The Alpine Club reacted immediately and installed a water treatment system with a filter and an additional UV lamp in the Rotwandhaus to kill off non-filterable, heat-resistant germs such as rotavirus.

Due to their location in the mountains, huts are only very rarely connected to the public drinking water supply. If their water comes from deep-lying springs, it is filtered naturally from the ground. However, it is mostly surface springs that are tapped, which are fed by melt water and rainwater. And these are easily contaminated with bacteria and germs due to excrement from cows and wild animals. Climate change is also a growing concern for hut owners. Long dry periods are followed by heavy rainfall. Even then, it can happen that cloudy water comes out of the tap in the hut because sediment clogs the filter system. Then even UV radiation no longer helps.

Interview with a drinking water expert

But what about the springs that bubble up from the ground or rocks along the way? Is it safe for cyclists to fill up their water bottles? We asked drinking and waste water expert Dr Claudia Beimfohr from Vermicon AG in Munich.

"You don't catch norovirus from cows."

BIKE: The tap in mountain hut toilets often says "No drinking water". So this isn't a trick by the hut warden to prevent you from filling up your water bottle for free?

Dr Claudia Beimfohr(laughs) Of course, it's possible that a landlord uses such tricks. But if a water treatment system including a UV lamp is installed in the hut, you can drink the water without hesitation. However, such a system is not uncomplicated. The filters must be changed in good time and a UV lamp must be optimally adjusted to the required water penetration. As soon as the water contains more sediment, the irradiation must be extended. However, it is also possible that such treated water is only used in the kitchen and shower and unfiltered water is used in guest toilets.

If UV rays are able to kill even heat-resistant germs and viruses, then drinking from a clear mountain stream shouldn't be a problem at all?

However, UV light has a very low penetration depth of 5 to a maximum of 10 centimetres. An irradiation time of 3 - 5 seconds is required to kill germs effectively. With very clear water and full sunlight! If there is sediment in the water, it takes longer. This is not possible in flowing water.

Suppose I fill a transparent water bottle with clear stream water and put it in the bottle holder. Will the sunlight be enough to kill the germs? You often see this with survival experts.

For this variant, it would be best to fill the water into the bottle through a cloth to filter out suspended particles. Even the smallest suspended particles in the water can bind germs and greatly hinder the UV rays. It would also have to be a transparent PET bottle because glass does not allow the important rays to pass through. And then this bottle would have to be exposed to full sunlight for 6 hours. If there are only occasional clouds in front of the sun, the procedure takes two days and on very cloudy days nothing happens.

But let's be honest: I've often drunk water from a mountain spring and have never caught a norovirus.

You won't catch norovirus in flowing water because of possible cow faeces. Although there is a similar virus in cows, it is harmless to humans. The highly infectious noroviruses and rotaviruses are transmitted from person to person. Via aerosols, i.e. through the air we breathe, or as a smear infection. But there are of course plenty of other bacteria, viruses and germs in the water that are not good for humans. In the end, it's a matter of luck as to how many pathogens you catch.

Which water can you drink in the mountains with a clear conscience?

Wells are a good source because you can assume that they have been drilled deep enough and the water has undergone natural soil filtration. From a depth of 10 metres, the water is said to be very well filtered. If the soil also contains clay for slow percolation and clay minerals, even viruses are filtered out. Wells that are not deep enough or have been drilled into rocky, sandy, i.e. quickly permeable soil, are hopefully always labelled "No drinking water".

What is the worst thing that could happen to me if I drink contaminated white water?

Severe vomiting-diarrhoea. This sets in after about 10 to 24 hours and can lead to dehydration if you are in poor physical condition and/or have a weakened immune system.

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