We’ve all seen the classic film or cartoon image of a dehydrated man stumbling through the desert in torn clothing, kicking up dust with every scuff of his worn-out boots. He’s sweating bullets, trying to suck the last drop out of a dirty canteen, and gasping, “Water! Water!” The sun is a huge fireball in the sky, and the heat is shimmering off the ground like it’s alive. While this image is great to convey high drama in the movies, a dehydrated pilot or aircraft maintenance technician can take on a much less theatrical profile: one you probably see more often than you think.

As helicopter professionals, much of the work we do, and the environments in which we do it, expose us to a greater-than-average rate of dehydration. In summer, we have those hot, sunny days where pilots spend hours strapped inside a poorly vented greenhouse, while maintenance personnel ply their trade on simmering asphalt tarmacs. Then, we have the great northern winter, with temperatures of 40 degrees Celsius (40 Fahrenheit) or colder, often accompanied by high winds. The air is unbelievably dry, and simply putting the aircraft covers on in the evening could result in clinical dehydration (more about this later).

Given its importance and how little many in the industry know about it, this article will discuss some critical basics, including how and why our bodies use moisture, and the mechanics of how dehydration occurs, its effects on our performance and health, and how we can prevent it in our working environment.

The human body is primarily composed of water, about 60 percent, in fact. To put this in perspective, a 200-pound (91-kilogram) man will contain approximately 55 liters (14.4 US gallons) of water in and around all the cells of his body, and in his bloodstream. This water is used for virtually every function the human body performs – regulating temperature, eliminating waste, undertaking digestion, and transporting nutrients and disease-fighting agents. Water even plays a role in neurological functions and the thought process; it is truly what keeps us alive.

Water enters our bodies when we eat and drink, and exits in three primary ways – urination, perspiration and transpiration (through the breath) – but we can also lose certain unexpected amounts of fluids through vomiting, diarrhea, excessive mucus production, etc. Under just normal circumstances, a body will lose between two and 2.5 liters of fluids in a 24-hour period, or about two to three percent of total body weight for that 200-pound man.

As just mentioned, we use water in virtually all of our metabolic processes. Urination is one way our bodies dispose of waste, and urine is a good indicator of our state of hydration. Clinically speaking, a healthy, hydrated person should have “clear and copious” urine, with a yellowish tint caused by a pigment called urochrome. Dark yellow and often pungent-smelling urine is an indication that you need more water. This will often be your first sign of dehydration, even before you get thirsty. The use of diuretic substances like alcohol, certain pharmaceuticals, caffeine and many carbonated soft drinks, increase the production and excretion of urine, and will have a major impact on hydration. Be aware that when consuming these products, the urine may be “clear and copious,” but fluid levels are being significantly depleted.

Less frequent, but still very significant, are the excessive fluid losses through diarrhea and vomiting. The average body loses approximately 200 milliliters (about 6.8 US fluid ounces) of fluids a day through normal bowel movements, but this can increase to several liters if the person is suffering from diarrhea.

Perspiration, which is one of the ways our bodies regulate temperature, is another large consumer of fluid reserves. When the brain senses an increase in body temperature, it takes action in two ways to bring the core temperature down. First, the body secretes the saline solution we all know and love, which cools the surface of the skin through evaporation. At the same time, there is increased blood flow to the skin as the blood vessels have expanded (vasodilation). The temperature of the blood is lowered as it flows through the cooled skin, then the newly cooled blood returns to the body’s core. There, it picks up excess heat, and the process continues until a satisfactory temperature is reached. External temperature alone can cause the body to heat up and perspire, but performing work will exacerbate the creation of heat, hence we sweat more when working hard.

There are some keys facts to know about perspiration:

It only works when the sweat can evaporate, so tight clothing or that which doesn’t “breathe” will hinder cooling.

There is no cooling benefit when perspiration drips off or is wiped away; it is wasted.

In high humidity, less evaporation occurs; therefore less cooling is achieved. This is why we feel hotter on a “muggy” day.

We also lose water when we breathe, as evidenced by breathing on your sunglasses before cleaning them, and by the ability to see your breath when it’s cold. In fact, it’s during cold, dry weather that we lose the most moisture through transpiration. In the Arctic winter, steam doesn’t form on the mirror when showering, lips and skin develop painful cracks, humidifiers need constant filling, and static electricity in day-to-day life can be almost unbearable. I have vivid memories of getting out of the shower, reaching for a towel, and then realizing I didn’t need to use it as I was already dry. In this environment, cold, dry air is inhaled and warmed by body heat. The warm air absorbs moisture from the lungs and carries it overboard when we exhale. This can be a significant contributor to dehydration, made even more insidious by the fact that we don’t usually feel thirsty when it’s cold.

Now we know how and why water is lost, so what happens when it isn’t replaced?

The onset of dehydration appears in stages. After the loss of approximately 1.5 liters of water (a little less than two percent of the total body weight of that 200-pound man), we begin to feel thirsty. At the three-liter point, we’re getting sluggish, tired, maybe nauseated and irritable – a very dangerous level for pilots, as this is where your faculties start to become affected, but you may not be aware of the deteriorated performance. United States Army experiments on helicopter pilots clearly indicate that self-reporting is notoriously inaccurate, even at relatively early stages of dehydration. In the tests, aircrews that reported feeling no adverse effects had clear, objective difficulty with cognitive tests.

By the time the body is four liters low, it has entered a stage of clumsiness. Headaches are likely, along with an increase in core temperature, heart rate and breathing rate. At this level or beyond, you have ceased to function effectively, as coping with the fluid loss becomes the body’s priority (see Table 1).

Suffering from one serious episode, or several repeated moderate episodes, of dehydration can result in kidney stones, which are stone-like masses of mineral salts. Kidney stones can cause intense, incapacitating pain when passing through the urinary tract, as well as other symptoms like fever, chills, blood in the urine, nausea and vomiting. There are several manners in which kidney stones may be treated. Shock-wave lithotripsy literally pulverizes the stones into smaller pieces that can be passed more easily. Other methods are a little more invasive… if you get my drift. Diagnosis of a kidney stone may have an effect on pilot license privileges. Anyone who has ever had stones will tell you that one of the last places you want to be during an attack is flying a helicopter – as mentioned, the pain can be overwhelming and debilitating.

Thankfully, simply keeping the body well hydrated can prevent stones in most people. A friend who suffered a bout of kidney stones a number of years back is rarely seen without his water bottle these days. I took it as a lesson learned.

So, we’ve determined that dehydration is a bad thing – how do we prevent it? Well, the simple answer is “drink plenty of water,” but we can do better than that:

1. Recognize environments where the risk of dehydration is increased.

2. Be aware of changing environments, like going from a cold climate to a warm climate or vice versa. The body can take up to two weeks to acclimatize to new climates, and during this time it may use more fluid reserves than it normally would. I recall getting off the plane during contracts in the tropics and immediately becoming drenched in sweat for the first few days. After the first week, my perspiration dropped to “normal” levels as I became accustomed to the climate.

3. Do not rely on thirst as the signal that you need water. By then, you’re already on your way to dehydration. In addition, drinking a small quantity of water, insufficient to rehydrate, may fool the thirst mechanism.

4. Carry a container or bottle that allows you to monitor how much fluid you drink.

5. Avoid excessive use of diuretics (e.g., caffeine, alcohol).

6. Monitor activities such as exercise or heavy work, and rehydrate accordingly.

7. Monitor your health state. Vomiting, diarrhea, fever and many illnesses like influenza or the common cold will all cause the body to lose fluids at a much greater rate than normal.

8. As a guide, drink enough water throughout the day to keep your urine relatively clear.

9. Plan to carry sufficient water, and ensure it is readily available. This can mean up to eight liters a day in some environments, or even more in extreme cases.

10. If water doesn’t do it for you, try a sports drink: they are great for replenishing fluids and restoring electrolyte levels, which may become depleted in episodes of heavy perspiration. If you find these drinks a tad expensive, or unavailable in your bush camp, make your own – here’s a recipe that works great:

1 liter (4 cups) of water

60 ml (4 tbsp) of sugar

A pinch of salt

125 ml (1/2 cup) unsweetened orange,  lime, grapefruit or lemon juice, or lime cordial to taste.

Preventing dehydration is important all year round. Cold, dry winter weather can deplete the body of vital fluid while we remain blissfully unaware. In summer, keeping the fluid reserves topped up goes a long way to help prevent another killer – heat exhaustion. And while that cold beer may seem like just the ticket after a long day of bucketing on a fire, or that third cup of coffee might be calling you on that chilly January morning, be sure that your water bottle (or dirty canteen) isn’t too far away.

Brad Vardy’s commercial career took him from the Canadian Arctic to Asia and Africa in light, medium and heavy helicopters. He followed that as a test pilot for Bell Helicopter and has held several positions at Transport Canada, including deputy chief pilot for the Canadian Coast Guard. He now has an aviation consulting company in Ottawa, Ont.