Lack of water produces fatigue, muscle stiffness, cramps and all the adverse brain power effects associated with low blood sugar levels. I know of two top international pilots who have “lost it” in flight and attributed it to dehydration. It is commonly believed that dehydration has been a factor in accidents in the past. I am sure that many pilots, including many of you, have suffered adversely, when flying due to dehydration. Do not underestimate the effects of our hot climate and the accelerated effects of the canopy and lower density altitudes.
The effects accumulate quite subtly and begin before take-off. Stay in the shade and keep covered as much as possible before flight. Wear long clothes. Avoid drinking tea, coffee and soft drinks as they repel the moisture uptake of the body. Drink an excess of water with the view to “super hydrating”. Do this slowly over a period of time for maximum uptake. Yes you will pee more but not as much as you think (unless you’re an elderly gent before the op!).
If you notice effects of dehydration or expect to fly for a very long time some sports drinks can help you hydrate or rehydrate by providing various salts and minerals. However, avoid the older types and those with high sugar content. Even then it is best to dilute them with 2 to 3 times their amount with water and drink them slower, using plain water in between. I find that mixing a third pure, unsweetened apple juice or dark grape juice in water provides you with a more pleasant and sweet taste in flight and the carbohydrates contained will better replace the energy you are burning.
You should pee during a glider flight, in hot conditions after 2 hours or so. If you don’t you are not drinking enough and you will be dehydrating. You may then encounter (although not notice – unless you are now more aware) tiredness, headachy, stiff and cramped. The pee should be clear – not like the diluted apple juice, If there is any yellowing or smell, drink more clear water.
Alcohol is not only a diuretic, but aviation medical research shows that its’ effects remain in the body for several days – with a resulting loss of mental abilities. However, we are presumably on “gliding holidays” so one glass or can per night is perhaps a compromise?