Planning / Safety / tips

Water stops on the TMB

One piece of advice I always give to my zoom clients is not to carry too much water along the Tour du Mont Blanc trail. This is a welcome piece of news, as compared to some other hut to hut treks – Italy’s Alta Via 1 for example (which is notoriously dry), the TMB has plenty of water sources.

I regularly see trekkers heaving at least 3 litres each, slogging it up the Col du Bonhomme panting with the effort of unnecessary weight.

Water weighs a lot! Did you know that 1 litre of water weights 1kg?

With refuges dotted every 5kms along the TMB route it’s actually not necessary to load up with water. All refuges apart from those mentioned below have a tap or a water trough where trekkers can re-fill their water bottles.

This water trough at Refuge Le Balme (stage 2) is right next to the trail and services both the free bivvy site here & passing trekkers

There are plenty of water troughs along the trail. Almost all water is ‘potable‘ (drinkable) however occasionally you may see a sign saying ‘l’eau non potable‘ – note that this means non drinkable.

How altitude affects your water intake

No trekker is the same in terms of how much they drink (and how much they sweat). It’s an individual choice as to how much water you anticipate needing, and indeed how much extra you want to carry … just in case.

The rule of thumb is to carry 1 litre for every 2 hours of hiking. You will need to adjust this amount according to temperature, trek intensity and altitude so I would tweak this to be a little higher for trekking the Tour du Mont Blanc trail.

Your body loses water through respiration twice as fast at altitude than at sea level so you should in theory be drinking twice as much water when trekking at high altitude. Now the TMB isn’t the Himalayas but much of the trail is above 1500m – the point when your body starts to work harder and your respiration rate increases. Something to bear in mind.

How much water do I need to carry?

I normally carry around 1.5 litres at any one time on the TMB, however I probably don’t drink as much as I should … but I sweat very little.

In general I would suggest carrying between 1.5 litres between towns and villages topping up to 2 litres when crossing a col.

I carry a 750ml water bottle as well as a small camel bak. I never carry just a camel bak as I always take rehydration salts every evening whilst trekking and also like to have a water bottle next to me at night when sleeping in the refuges. I’ll always use my camel bak water first whilst trekking – it saves time needlessly having to stop every time I need a swig.

For stages 10 and 11 or if I’m doing the variant stage 8 across the Col du Fenêtre, which is also lacking in water, I will fill will my camel bak to the brim. I discuss these stages in further detail below.

Water is untreated and unsafe to drink at Lac Blanc. Carry extra water on stage 10 or bring a water filter bottle

So where do I need to carry extra water on the TMB?

Stages 10 and 11

Stages 10 and 11 of the Tour du Mont Blanc are particularly dry. On these sections you need to either carry extra water, have a filter water bottle so you can re-fill at the lake, or at a last resort be prepared to buy bottled water from the refuges – not something we’re encouraging quite frankly. If you are desperate then know that Refuge Lac Blanc only accepts cash (euros).

Refuge Lac Blanc (on stage 10) and Refuge Bellachat (on stage 11) are often frustrated by trekkers demanding to have their water bottles refilled. These refuges are unable to offer free tap water refills – they just don’t have running tap water that’s drinkable.

Lac Blanc is not a natural source – only a melted pool of snow and ice. This water is not controlled, it has not been treated. Often people assume glacial water, snow or ice are pure, however ice can preserve pathogens and fecal matter – not something that is going to make anyone feel very good.

It’s the one thing that exasperates Marion, the warden at Refuge Lac Blanc. “Some hikers just don’t get it – some get cross when we tell them we can’t re-fill their water bottles! The water is just not safe to drink”.

Refuge Lac Blanc is unable to re-fill your water bottle. Come prepared!

Stage 8 variant

Variant stage 8 is also very dry so you need to carry extra water and actually here it’s different to stage 10 in that there is no water source to fill up from so a filter water bottle here is useless.

If you are planning on taking this variant trail via the Col du Fenêtre from Champex Lac to Trient/La Peuty its good to know that there is nowhere to fill up at all after Refuge Relais d’Arpette until the Bisse du Trient (the balcony walk just before descending down into La Peuty, Trient or continuing on to Hotel de la Forclaz).

The Buvette du Glacier mountain café on the descent from the col does not have free potable water to refill your flask but does sell water. For those with filter water bottles you can fill up here from the glacial stream.

Water trough on traditional stage 1 from Les Houches to Les Contamines

Can I drink from the streams on the TMB?

It’s not advised to drink from the streams along the TMB. You’ll see plenty of cattle or sheep grazing along much of the TMB route which means there’s a high chance of fetal matter polluting the water courses.

If you have a filter on your water bottle or have water purification tablets with you then, of course, you can use the stream water to fill up however in most cases its just not necessary because of the flux of water troughs along the trail as well as refuges every 5km.

I’m regularly asked by zoom clients if they should bring water purification tablets. I don’t think this is necessary. On the few sections that are dry – just carry an extra litre of water.

Water troughs on the TMB

Most water stops on the TMB are via outside taps at refuges or traditional water troughs – some dating back centuries.

Water troughs can be simple – roughly hewn from wood in more remote areas or whilst you’re walking through villages or towns you’ll see grander affairs made from stone . One of my favourite water troughs, on the beginning of stage 5, dates back to 1889. You’ll see this on the right hand side on the ascent as you leave Courmayeur.


  • Elizabeth
    September 26, 2023 at 2:20 pm

    Thank you Mags! Incredibly helpful!!

  • TMB Wannabe
    January 31, 2024 at 11:12 pm

    The Elixir of life ! Thanks Mags


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