Water and Food for a Day Hike: How Much to Bring

1.5 liters, or about 1.6 quarts. That’s the minimum the French Hiking Federation (FFRandonnée) tells each hiker to carry on a summer mountain hike [1]. In the desert heat of Death Valley, the national park tells visitors to drink at least a gallon (about 3.8 liters) a day [2]. On paper, 1.5 liters doesn’t sound like much; in your pack, it’s 3.3 lb, a load that lightens as the day goes on. Let’s run the numbers, water first, then food.

Water: how much to carry, and how to drink it

The baseline is simple: the federation asks for enough water and food, at least 1.5 liters of water per person, and for eating and drinking regularly on the trail [1]. The Swiss Council for Accident Prevention (BFU) puts it its own way: drinks are heavy, but you can’t do without them, and they get lighter as you go [3]. So don’t skimp on water to save a couple of pounds: it’s the most useful weight in your pack.

1.5 liters is a floor, not a goal: a long day, a big climb or a blazing sun pushes it up. The Park Service’s Ten Essentials list includes water treatment supplies, and asks you to check before you go for water at your destination that you could collect and treat [4]; more on treating it below. When in doubt, an extra bottle weighs less than an afternoon with an empty one.

Timing matters as much as quantity, and here official advice doesn’t quite agree with itself. The BFU says to drink plenty even when you’re not thirsty [5]; the Ten Essentials page, to drink water often and before you feel thirsty, especially in hot weather [4]. Grand Canyon and Joshua Tree say don’t force fluids, drink when you’re thirsty [6, 7]: drinking too much water while losing salt through sweat can cause hyponatremia, low sodium in the blood, Grand Canyon explains, so it pairs regular sips with salty snacks [6]. The common ground: a few sips at every break, not half a bottle at the summit.

In hot weather

Heat changes the math. Grand Canyon National Park tells summer hikers to stay off the trail between 10 a.m. and 4 p.m., with a predawn start and a late-afternoon finish; most of the people who need emergency medical help in the canyon for heat illness are hiking during those hours [6]. Joshua Tree says to avoid hiking between 10 a.m. and 5 p.m. in summer [7]. Both parks call for plain water plus some electrolyte replacement, and for salty food, twice as much as you’d normally eat [6, 7]. Grand Canyon adds that hikers can lose 1 or 2 quarts (liters) of water an hour through heavy sweating, the road to heat exhaustion [6].

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Refilling on the trail: filters, filter bottles, and tablets

A dry spring, a detour, a hot day that doubles your thirst: your bottle can run dry before the hike’s over. That’s why it pays to carry a way to make creek water safe to drink, because clear water isn’t necessarily safe: the CDC warns that drinking straight from a sparkling mountain stream is generally not safe [10].

A hiking 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 [10]. Purification tablets work almost the other way around: they kill bacteria and viruses, but not always parasites, and chlorine dioxide needs several hours of contact time to deal with Cryptosporidium [11]. When you can’t boil the water, the CDC recommends filtering it, then disinfecting it [10].

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Two more precautions: the instructions for your bottle or filter should list an absolute pore size, not just a “nominal” one [10], and a hollow-fiber filter that has frozen can let germs through with no visible sign [12]. Our guide to finding and treating backcountry water walks you through every method, from boiling to UV light.

Food: the energy cost of a day on the trail

On the energy side, the Compendium of Physical Activities, a database published by researchers, measures effort in MET (metabolic equivalents): 1 MET is defined as 1 kilocalorie (what a food label calls a calorie) per kilogram of body weight per hour, roughly what you burn sitting quietly [13]. 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 [14]. For someone who weighs 154 lb (70 kg), that works out to 266 to 420 calories an hour, or about 370 to 420 for an hour of real hiking.

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These numbers count everything, including what your body burns at rest, and they’re for hiking without a load: the Compendium rates hiking with a daypack higher still [14]. Treat them as a ballpark, not a ration to weigh out. Mostly, they explain why the French Hiking Federation says walking calls for more food than resting, matched to how long and how hard you go: nothing excessive, but enough energy, taken in regularly, so you don’t run out of gas [15].

Eat a little, often

The federation’s golden rule: light, small, nutritious food, eaten regularly on the move to keep your blood sugar steady [15]. The BFU recommends a break every 1 to 1.5 hours to rest and refuel [5]: the right rhythm for a few bites and a few sips.

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On an easygoing hike, lunch is one of the best parts of the day: the federation suggests a balanced meal with complex carbs such as bread or starchy food, protein such as a hard-boiled egg, lean ham or cheese, fresh vegetables, and fruit that travels well [15]. For the in-between, the Park Service’s Ten Essentials list favors salty, easy-to-digest snacks such as trail mix, nuts and granola bars, plus an extra day’s worth of food in case your plans change [4].

• When your blood sugar drops: an energy bar, dried fruit or chocolate brings it back up fast; nuts, whole-grain bread, cheese, meat or eggs give longer-lasting energy, according to the BFU [5].
• What to avoid: food that spoils quickly (eat it first if you bring it), heavy, bulky cans, anything that gets crushed in your pack, food with too little energy in it, and alcohol, which the French Hiking Federation bans from your pack outright [15].
• Packing it: light and compact, with snacks within easy reach, as our day hike packing list explains.

It’s no accident that the National Park Service’s Ten Essentials give two of their ten slots to food and water: extra food, and water with a way to treat it [4]. Without them, the best planning won’t get you far. For the rest of your prep, our guide to planning a hike walks through the steps one by one.

Worth watching

The Grand Canyon’s official nonprofit partner on drinking and eating enough, and timing a hike around the heat, in five minutes: the same advice this guide cites from the park.

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Julien de Jurquet

Vans, RVs, biking and calculators

Julien de Jurquet writes for Outfarer about camper vans, RVs, biking, and calculators. He reads manuals cover to cover and never lets a number slide without its unit, so your choices rest on math, not promises.

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