Water and food for a day walk: how much to carry

1.5 litres. That is the minimum amount of water the French Hiking Federation (FFRandonnée) asks each walker to carry on a summer walk in the mountains [1]. The kit lists of AdventureSmart UK, Mountaineering Scotland and Mountaineering Ireland put water and food on the list without committing to a number [2, 3, 4]. On paper, 1.5 litres sounds modest; in the rucksack, it is 1.5 kg, a weight that shrinks as the day goes on. Let’s do the sums, water first, then food.

Water: how much, and how to drink it

The baseline is simple: the French Hiking Federation asks walkers to bring enough water and food, at least 1.5 litres of water per person, and to eat and drink regularly as they go [1]. The Swiss Council for Accident Prevention (BFU) makes the same point in its own way: drinks are heavy to carry, but they are indispensable, and they have the advantage of getting lighter as the walk goes on [5]. So there is little sense in skimping on water to save a kilo: it is the most useful weight in the rucksack.

1.5 litres is a floor, not a target. A long day, a big climb or a hot sun pushes it up: look on the map for streams and springs where you can refill, and carry a way to treat the water (more on that below). If in doubt, an extra bottle weighs less than an afternoon with an empty one.

Timing matters as much as quantity. The BFU advises drinking plenty, even when you are not thirsty [6], and the NHS suggests drinking enough through the day for your pee to stay a pale colour, and more when you sweat in hot weather or during exercise [7]. In practice: a few mouthfuls at every stop, rather than half a bottle in one go at the summit.

In hot weather

Heat changes the sums. The NHS counts walkers, along with runners and cyclists, among the people more vulnerable in a heatwave; it advises staying in the shade, especially between 11am and 3pm, avoiding activity that makes you hotter, and drinking extra fluids, but no alcohol, caffeine or hot drinks [8]. For a walk, that means an early start and the middle of the day spent in the shade. At the Grand Canyon, where summers are extreme, the US National Park Service asks hikers to carry water and something to replace electrolytes, to eat salty food often, twice as much as usual, and to sip water regularly all the way, even without feeling thirsty. It also warns against forcing fluids: drinking too much water while losing salt through sweat can lead to hyponatraemia, low sodium in the blood [9].

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Refilling on the way: filters, filter bottles and tablets

A dry spring, a detour, a hot day that doubles your thirst: the bottle can run dry before the walk is over. Hence the case for carrying a way to make stream water drinkable, because clear water is not necessarily safe: drinking straight from a sparkling mountain stream is generally not safe, warn the CDC, the US public health agency [12].

A walking filter, whether pump, squeeze or built into a filter bottle, stops whatever is bigger than its pores: at 0.3 micron absolute or less, parasites and bacteria, but not viruses [12]. Purification tablets work almost the other way round: they kill bacteria and viruses, but not always parasites, and chlorine dioxide needs several hours of contact to deal with Cryptosporidium [13]. When you can’t boil the water, the CDC therefore advise filtering it, then disinfecting it [12].

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Two more precautions: the instructions for the bottle or filter should give an absolute pore size, not just a ‘nominal’ one [12], and a hollow-fibre filter that has frozen can let germs through with no visible sign [14]. Choosing a method, from boiling to UV light, is covered in our guide to finding and treating water.

Food: the energy cost of a day’s walking

For energy, the Compendium of Physical Activities, a reference database published by researchers, measures effort in MET (metabolic equivalents): 1 MET is defined as 1 kcal per kilogram of body weight per hour, roughly what you burn sitting quietly [15]. Hiking at a normal pace through fields and hillsides, with no load, rates 5.3 MET; cross-country hiking, 6 MET; ambling, 3.8 MET [16]. For someone weighing 70 kg, that gives 266 to 420 kcal an hour, or around 370 to 420 kcal for an hour of proper walking.

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These figures count everything, including what your body burns at rest, and they are for walking without a load: the Compendium rates hiking with a day rucksack higher still [16]. They give an order of magnitude, not a ration to weigh out. Above all, they explain why the French Hiking Federation points out that walking calls for a richer diet than resting, adjusted to how long and how hard you go: no needless excess, but enough energy, taken regularly, to avoid running out of steam [17].

Eat little and often

The French Hiking Federation’s golden rule fits in three words: light, small and nutritious, with food eaten regularly as you walk to keep your blood sugar steady [17]. The BFU advises a break every hour to an hour and a half, to rest and get your strength back [6]: the right rhythm for a few mouthfuls and a few sips.

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On a leisurely walk, lunch is one of the best moments of the day: the federation suggests a balanced meal with complex carbohydrates such as bread or starchy food, protein such as a hard-boiled egg, lean ham or cheese, salad vegetables, and a few pieces of fruit that travel well [17]. In between come the snacks: dried fruit, cereal bars (avoiding chocolate ones when the sun is strong) and biscuits that aren’t too sweet [17]. AdventureSmart UK puts it more briefly: high-energy snacks, for a boost when you tire, and a flask of hot drink [2].

• When your blood sugar drops: an energy bar, dried fruit or chocolate brings it back up quickly; nuts, wholemeal bread, cheese, meat or eggs give longer-lasting energy, says the BFU [6].
• What to avoid: food that spoils quickly (eat it first if you take it), heavy and bulky tins, anything that gets squashed in the rucksack, food with too little energy in it, and alcohol, which the French Hiking Federation bans from the rucksack altogether [17].
• Packing it: light and compact, with the snacks within reach, as our day walk kit list explains, plus a bag for the leftovers: Mountaineering Ireland asks walkers to take all their litter home, fruit peel and tea bags included [4].

Mountain Rescue England and Wales points out that many accidents happen towards the end of the day, when both you and your phone are low on energy, and its safety advice is to eat well before you start and all through the day [11]. Water and food keep the rest of the plan working. For everything else, our guide to planning a walk takes the steps one at a time.

Julien de Jurquet

Campervans, motorhomes, cycling and calculators

Julien de Jurquet writes for Outfarer about campervans, motorhomes, cycling and calculators. He reads instruction manuals to the very end and never lets a figure through without its unit, so that your choices rest on sums rather than promises.

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