Staying hydrated is just about your first priority on any wilderness trek. You can go weeks without food, but mere days without water, and even a moderately dehydrated person may get sufficiently fogged-up in the cognition department to make poor, even dangerous choices.

On day hikes and overnighters, you can often get by toting all the water you need from home. But that's not feasible for backpackers on multi-night treks, who'll need to find and treat natural water sources along their way. Really, though, everybody - including day hikers - should have some idea of how to find water on a given landscape: After all, you never know when you might be lost or stranded, and it's also easy to underestimate your own water needs, especially in hot conditions.

Here are a few tips for how to find water in the wilderness and for warding off dehydration.

The Importance of Staying Hydrated While Hiking or Backpacking

It's impossible to overstate the importance of water, which after all makes up most of a human being - about 60 percent or so for the average adult body, and 90 percent of our blood - and facilitates innumerable vital biochemical processes that keep us alive.

Some of us struggle to stay hydrated in our everyday lives at home or at work; it's all the more difficult in the great outdoors, when our enhanced physical exertion and greater exposure to the elements translate to more significant and continual water loss.

Dehydration is an insidious condition. It sneaks up on you: If you're thirsty, there's a good chance you're already mildly dehydrated. Many symptoms we attribute to normal tiredness on the trail and altitude sickness at higher elevations are in fact signs of dehydration. These include headaches, fatigue, nausea, and low-grade crankiness.

Left unaddressed, dehydration can worsen into more serious effects - accelerated heart rate, pronounced weakness, mental impairment - and increase to a severe state of fluid deficit that may be impossible to remedy in the backcountry.

Furthermore, drinking too little water can exacerbate other issues. "Dehydration is a contributing factor to hypothermia, heat exhaustion, heatstroke, altitude illness, and frostbite," Tod Schimelpfenig and Linda Lindsey write in the National Outdoor Leadership School's Wilderness First Aid handbook. "Dehydration worsens fatigue, decreases the ability to exercise efficiently, and reduces mental alertness."

Typical Water Needs on the Trail

As a general rule of thumb, you should drink about a quart of water per hour of hiking. Some reckon your desired average daily consumption on the trail to about a gallon. Clear urine is a rough-and-ready sign of adequate water consumption; a darker hue suggests you're dehydrated.

A quart of water in a bottle weighs about 2.2 pounds, so it's easy to see how the weight of the water can add up quickly in your pack. Using one or two water bottles, a soft-bodied water bag, and/or a bladder, the trick is to carry an adequate amount to meet your needs and keep you hydrated between water sources - not too little, not too much. This requires a clear idea of how to track down water on the landscape.

How to Find Water in the Wild

Use multiple resources to cross-reference information on where you're likely to find water in the area you'll be hiking/backpacking in. Those include topographic maps, aerial photos, guidebooks, online hiking forums, and information gleaned from park/forest rangers and other local authorities. The latter personnel can also clue you in to any current concerns about water quality in a given area.

A topo map of adequate scale will directly indicate likely water sources such as rivers, creeks, lakes, ponds, and springs, but you can also study the illustrated terrain and, considering it against the season, note where other possible sources may exist. Those might include lingering snowfields, trickles in a draw or gully and pools in hollows or bare-rock potholes after a wet stretch, and seeping slopes, banks, or ledges.

Speaking of seasonality, it's definitely an essential consideration when planning a hike around water sources. Many streams are seasonal or ephemeral; such flows are often indicated with stippled blue lines on a topo map, but if conditions have been especially dry even creeks marked in solid blue may be nonexistent. In the early summer, mountains may have plentiful snowdrifts and patches to melt water from; by late summer, they may be dry and dusty.

Plan ahead for multiday backpacking so you can structure your route with regular replenishment of your water supply, using your estimated water consumption and the layout of water sources to come up with the gameplan. If you have a long (say, 20-plus miles) stretch of apparently waterless trail, consider splitting it into a couple of days so you can take advantage of cooler, less sweat-inducing walking in the late evening and early morning. Be realistic about how much ground you can cover and how much water you might have to consume; even if you're within view of a river, it can be an annoying or downright taxing effort to hike down for water if nighttime catches you on a ridgetop thousands of feet above it and with your water bottles/bags empty.

Finding Water for Survival

If you're out of water and either unsure of where the nearest source is or excessively far away from the closest mapped source, you need to key into as many natural clues as possible to make searching water out as efficient and least-strenuous as possible. We've already mentioned some of the more subtle locations of water on the landscape, including tiny seeps and snowfields sustained in the deep shade of a north-facing hollow or tree grove. Take some time to study your map - if you know your location, that is - and identify promising water-catching and water-holding terrain and land-cover features.

Depending on the lay of the land, mid-morning and early evening can be good times to spot the glint of water at a distance - a pool, a brook, a marsh - from some kind of elevated vantage. Such a vantage (and such times of day) is also good for spotting flocks of birds or swarms of insects that might be congregating at a water source, and for catching the distant sound of running water.

In the morning or in misty conditions, you can often wring dew from vegetation using a bandanna or a piece of clothing. You can also make various forms of stills, including pit-dug solar stills and plastic bags or sheeting wrapped around sun-exposed greenery with a weighted corner for collecting the transpired water. At the outside bend of a desert wash or in coastal sand, you may be able to find water by digging a hole several feet down and waiting for it to accumulate groundwater.

Treating Water in the Backcountry

If you're in desperate survival straits and don't have the ability to purify water, you should drink it anyway - the risk of illness is a risk worth taking if you're facing severe dehydration. In any other case, though, you should play it on the safe side and treat natural water sources. It's a classic bone of contention among backpackers, hunters, and other wilderness travelers, and many argue you can drink freely with confidence from backcountry springs and alpine streams. But given you should own a good water filter or purifier anyhow and use it for lower-elevation and otherwise sketchier water sources, it doesn't hurt to simply treat any water you're drinking in the wilderness.

We've published a primer on water purification here at the Mountain House blog, which we suggest eyeballing next!