I would like to start this with I am a physiological zoologist and thermal biology is my speciality. I have also spent a lot of time walking and motorcycling in remote places. For example on one trip in the Oz red desert (temp= 43°C and MMH = 0) I drank 10lt of water in 7 hours. I never went to the toilet and was dry as a bone (no sweat) and even after that my urine was dark!. The desert rule of thumb is 5-8l per person per day Plus 2 days emergency supplies. When working, you should drink up to one litre of water per hour of “exercise”, on top of your normal daily amount. I know this can be hard on a bike, but 1.5-3lt per day is not enough for working conditions. 1-2 lt is the recommended amount for sitting around watching telly in the UK.

Water is the most important thing to carry. Even when "not working hard" but being on a motorcycle water is literally pulled out of your body (this is both conductive and convective evaporation). Many people use this dry their cloths. If you don’t believe me try it, next time it is not actually raining (can you tell I live in the UK now) wet a cloth and hang it off your bike go for a ride and it will be dry faster they you can imagine, NOW increase the temp and lower the humidity. Your skin will be acted on the same way, in order to keep your skin cells alive more and more water will be supplied to them. If you are sweating to keep your core temperature down, (this can kill you too), you are losing it at a much more rapid rate because you are actually trying in increase evaporative cooling.

The human body is about 70% water and we have a small reserve of water and can lose some without any effects. However, dehydration occurs when there is a 1% or greater reduction in body weight due to fluid loss. And really it is defending against dehydration that we are really discussing here. So for a 100kg person that is one litre, 40kg person that is 400ml. NOT A HELL OF A LOT!

Clinically speaking depending on the percentage of body weight lost, dehydration can be described as mild, moderate or severe. Mild dehydration - is a relatively low level of fluid loss (causing a 1-2% loss of body weight) can cause the body to work less efficiently. However, mild dehydration carries few long term health risks and can usually be easily treated by replacing lost fluids. But can decrease your reaction times, concentration and minor weakness; all of which could be deadly on a bike. Also even minor chronic (ongoing) dehydrationit can affect kidney function and may lead to the development of kidney stones. It can cause dry, wrinkled skin and be harmful to your liver, joints and muscles. It can also cause cholesterol problems, headaches, reduced blood pressure (hypotension), fatigue and constipation.

After a loss of about 2.5%of body weight, significant neurological impairment is noticeable; Sever loss of concentration, syncope (dizziness), market weakness, muscle cramps and more.

Moderate dehydration - is a 3-5% decrease in body weight due to fluid loss. This level of fluid loss can result in a substantial decrease in strength and endurance and is the primary cause of heat exhaustion.

Severe dehydration - is a decrease of more than 5% of body weight due to fluid loss. A 10% or greater reduction in body weight is extremely serious. If not treated immediately, this level of dehydration can be life threatening. Hospitalisation and an intravenous drip may be necessary to restore the substantial loss of fluids.

It is important to remember that thirst is not a good indicator of dehydration. If you are thirsty, you are already likely to be suffering from the effects of dehydration!!!!

The signs of dehydration in adults include:

* dry mouth (xerostomia),
* chapped or dry lips,
* dry eyes,
* dry, loose skin with a lack of elasticity,
* sunken features, particularly the eyes (enophthalmos),
* clammy hands and feet,
* headaches,
* light-headedness,
* dizziness,
* tiredness,
* confusion and irritability,
* loss of appetite,
* burning sensation in your stomach,
* feeling of an 'empty stomach' or abdominal pain,
* low urine output, and
* concentrated, dark urine with a strong odour.


When travelling, we may suffer added pressures then just environment conditions. Dehydration often results from an illness, such as gastroenteritis, where you have persistent diarrhoea and vomiting. You can also become dehydrated after sweating excessively from a fever. Dehydration can also occur from drinking too much alcohol. The headache associated with a hangover indicates that your body is dehydrated. This is why it is important to drink plenty of water when you have been drinking alcohol. Certain drinks: some teas, coke, coffee (he says while drinking his 4th cup) are diuretics and will increase your water loss, so these will not help as well.

Finally changes in salt content in our diet can also have an impact of the fluid transport (i.e. if you take in a lot of salt you need more water to clear it) n rare cases, it is possible to over hydrate. This condition, known as hyponatremia, is low sodium, and can occur when too much water is drunk in a very short time. The condition sometimes affects endurance athletes whose blood sodium is reduced through sweat and then further diluted by drinking large amounts of water. Typical symptoms of hyponatremia include; nausea, vomiting and headache. In the most serious cases, the brain swells causing confusion, seizures, coma and even death. This is what caused the creation of “Sports Drinks” they are usually high in sodium and potassium both of which are lost when exercising and sweating. The scientific community is out on the efficacy of these for “normal” people even in high temp /low humidity areas.


I could go on for days about this... so I'll leave it with: The survival rule of thumb in normal conditions is; 3 days without water, 3 weeks without food. Bottom line: Carry as much as possible.. drink as much as you can..

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2000 Africa Twin
http://two-up-ona-twin.blogspot.com