Incredibly, the human body is mostly water, about 50-70% for males and 40-60% for females. Hence, adults have 30-40 kg of water. A loss as small as 2% of this water may have serious effects on performance[note]Montain, S. J. (2010). Water requirements and Soldier hydration (Doctoral dissertation, US Army[/note], so staying well hydrated is critical for feeling good and performing well on a bushwalk.

Water comes from fluids and foods with high water content such as fresh or tinned fruit. Water loss occurs through sweat, urination and respiration. Water intake and water loss is a delicate balancing act that can easily get disrupted under changing weather conditions and hard physical work.

Sweat increases due to hotter air temperature, higher humidity, more exertion or a combination of these. Sweat is the body’s cooling mechanism; sweat resting on the skin surface cools the skin. But it comes at a price: loss of body water, triggering thirst, and a desire to drink and replenish body water. Water loss due to sweat is far lower when resting in shade and when there’s more wind chill.

Wet bulb globe temperature (WBGT) is a ‘feels like’ temperature based on actual temperature plus humidity, wind chill and shade. WBGT provides a more accurate indication of the temperature as perceived by humans. Probable WBGT can be used to plan which walk to do and how much water to carry.

US Army guidelines give a good indication of water needs[note]Montain, S. J. (2010). Water requirements and Soldier hydration (Doctoral dissertation, US Army)[/note], translating well to Australian bushwalks.

Under spring conditions (WBGT = 15-25°C), bushwalkers carrying a pack of under 10 kgs require about 0.5 L of water for every hour of walking. So a typical 4 hour spring day walk means that 2 L should be drunk. However, it only takes an increase of 5°C (WBGT) for the water requirement to increase by 50% to about 0.75L of water for every hour of walking.

Once the WBGT exceeds about 32°C, water requirements are about 1 L per hour, and extended walking may become impractical. Under such conditions, walks should have ample supplies of reliable water at regular intervals, with distances and climbing shorter if at all possible. Another option is to walk during the cooler parts of the day.

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Staying well hydrated is paramount on a bushwalk, and in turn, looking after water supplies.

There are many ways to carry water, ranging from small to big, no cost to expensive. The most important aspect is reliability – the container must not break.

Careless packing of water bottles not only makes for harder walking but also can damage them, leading to leaks. Take the time to pack carefully and protect precious water supplies before heading out on a bushwalk.

There are three main types of bottles used by bushwalkers.

• Soft drink bottles
• Hard shell bottles
• Hydration bladders

Soft drink bottles are easy to drink from and readily available, but can get crushed more easily than a purpose built water bottle. They’re cheap and a great option for getting started bushwalking.

A hard shell bottle is more durable and reusable, and generally easy to fill than a soft drink bottle because the mouth is slightly wider. However, some people find the wider mouth can actually make it harder to drink from. Priced around $15 per bottle, they’re a pricey but reliable option in the bush.

Hydration bladders are becoming increasingly popular. They’re easy to drink from on the move and can be packed in the backpack so that the weight distribution is optimally set-up. The downside is that it can be hard to gauge how much has been drunk, so there’s a risk of running out of water. They’re also pricey (~$60), and the user should carry a
repair kit in case they spring a leak. But while it takes time to get comfortable with it, but it’s a great way to stay well hydrated in the bush.

The spine, hips and legs are best adapted for carrying significant weight. Packing weight into a backpack so that heavy items are distributed along the spine is the most efficient way of carrying weight and the best place to store water supplies. Most modern backpacks have a sleeve for water bladders that lies close to the back.

Water bottles and hydration bladders do occasionally puncture when treated roughly: take care to handle backpacks carefully. For this reason, carrying several small water bottles is generally better than one large one because there are backups. Importantly, if fuel and water are stored in the same sort of container, then it’s critical that the fuel container is suitably labelled.

Several small water bottles also give more flexibility in packing. Keep a small bottle handy near the top of the backpack for easy access: this makes it easier to remember to drink regularly. Alternatively, secure a bottle in an open side pocket with straps.

Practical tips:

1. Pack heavy items close to spine
2. Keep a small water bottle handy to reach
3. Secure any bottles on pack exterior

Keeping well hydrated is a balancing act between drinking enough to stay hydrated but not so much that essential salts are too diluted. While both can lead to serious medical conditions, they’re easy enough to avoid with proper planning and awareness.
Urine colour is a visual cue of hydration levels. In general, the better hydrated the body the lighter the urine colour.

The human body makes the best use of water when ingested in small amounts regularly, allowing time for water to be absorbed and used in the system. That’s why it’s important to drink regularly on a bushwalk. Hydration bladders make drinking small amounts regularly very easy.

Some people struggle to drink enough water. If so, try lightly flavouring water with cordial or setting a drinking goal, perhaps marking “drink-to” points on the water bottle. Note that flavouring water will render this water and perhaps the container unsuitable for meals or other drinks.

Caffeinated drinks like tea and coffee are mild diuretics, causing increased passing of urine. Drinking these can lead to dehydration if they’re drunk in large quantities or if the body isn’t used to them, but in small amounts such as on a bushwalk they provide similar hydrating qualities to water.

Due to the high sugar content, soft drinks and energy drinks are less effective at hydrating than water. High sugar concentrations in these drinks slows fluid absorption into the blood system. Some energy drinks also contain caffeine, guanine and preservatives which may have  negative effects on performance. Occasionally, people react badly to these kinds of drinks, so it’s best to try these at home first, or better – just stick to water!

Dehydration affects physical performance and occurs when the body loses water faster than it is replenished. When the overall body water content drops by 2%, dehydration signs and symptoms take effect.

If someone in the group has signs of dehydration, stop in shade and administer first aid. First, apply DRSABCD: check for any danger and make sure you are still getting a response from the patient (continue to – SABCD if necessary). Remove the patient’s hot clothing and encourage them to drink small sips of water. Consider shortening the trip and not walking in the hottest time of day, about noon-2 pm. Check all the party for dehydration and encourage everyone to drink.

Electrolytes are body salts necessary for our muscle and nerve function. As with body water, electrolytes too are lost via sweat, and must be replenished via eating healthy foods that are high in electrolytes. This applies in particular when bushwalking on hot days and when working hard.

In general, eating a balanced diet of fruits, nuts, vegetables and dairy is a healthy way of replacing salts such as sodium, chloride, potassium and calcium. This diet includes:

• Coconut water
• Leafy greens
• Tomatoes
• Celery
• Bananas
• Yogurt
• Nuts
• Beans

It’s not practical to carry some of these foods on a bushwalk, instead, stock up before and after the walk on items like yogurt and greens, and take nuts and fruit on the walk. Note that some food requires more water than others to digest.

There’s a huge amount of hype and media around sports drinks and their hydration power, although research shows there’s little difference between them and water. Their main selling point is to replenish electrolytes, although this is only needed for prolonged intensive exercise.
As sports drinks tend to be extremely sugary and filled with artificial flavouring, eating a balanced diet is a healthier alternative.

Hyponatremia is a rare condition that occurs when the sodium content in the blood is too low. This causes fluid to move into the cells making them swell, and has been known to be fatal.

Hyponatremia may occur by drinking too much water or losing too much salt (via sweat), but also from organ abnormalities or reactions to medication.

Signs & symptoms of hyponatremia include:

• Headache
• Muscle cramps
• Heart palpitations
• Decreased consciousness
• Confusion
• Fatigue
• Lethargy

On a bushwalk, if hyponatremia is suspected, follow the DRSABCD action plan and apply first aid. Stop and rest in the shade, and encourage the patient to eat something high in sodium (e.g. biscuits, chips) or pure salt (keep sachets in first aid kit). Monitor the patient and call for help if the situation deteriorates.

Although rare, hyponatremia is becoming more common due to people drinking too much when exercising. It must be treated seriously as it can be life threatening, just the same as drinking too little water. In short, it’s about getting the balance of water and salt intake right.

So on a bushwalk, drink well according to the body’s water needs under various temperature conditions, eat well and have fun!

Choosing when and where to walk under particular weather conditions can make a major difference to the amount of water needed by the human body. Water requirements increase dramatically as temperature and workload goes up. So selecting to walk in cooler conditions means less water loss via sweat and makes for a more enjoyable trip.

Choosing the time of day to walk can turn and exhausting mountain scramble, into a pleasant stroll up a hill. Select a route that tackles steep, exposed sections first or last in the day. During the heat of the day, find a shady lunch spot to rest and relax.

Wear light and loose clothing, nothing that sticks or irritates the skin. Select quick dry materials that still insulate when wet. Use sun protection and stop to re-apply sunscreen during the walk.

Last, and most importantly, slow down! Going as fast as possible not only exhausts the group, but it means they have less energy and incentive to enjoy their beautiful natural surroundings. People go to natural places for different reasons, but often it’s for many more reasons that getting from A to B: the journey is every bit as enjoyable as the end point, and slowing down allows more time to get to know the people in the group and relax.