• Hot water is less upsetting to your stomach than cold
• Small gulps of water often rather than large quantities seldom is much better for both your stomach and the hydration of youyr body
• You will naturally salt your food more heavily in hot climates, and extra salts in your water should not be deemed necessary, but do bring some rehydration packs for emergencies, or for when you really feel dehydrated. You'll know if you've got too little salt in your body if you feel you're dehydrated but still need to urinate a lot. At this point you are drinking enough, but your body won't absorb it.
• You know you are getting dehydrated if your urine is dark (it should be clear). Now you are drinking too little. At this point your concentration will drop, you will feel more exhausted, and you will get headakes... and big gulps of water won't make it go away, it takes time, and lots of fluids. Beyond this point, and you are getting into trouble. Rehydration packs, sport drinks, or even sweet soft drinks, will do you good.
• Go all out on the sweets, and have some salty nuts while you are at it.
• If conditions are extreme, cover your skin thouroughly to trap moisture/sweat, and protect your skin from the sun (touaregs walk all day on just a couple of cups of water, where as you drink like a fish on the same distance, and clothes play a big part).

As for tea, it does not contain caffein as suggested or as is commonly thought, but teeine (English spelling?). The chemical teeine is somewhat similar to caffeine, but from what I've heard, tea does not make you pee in the same way as coffee, as many people do believe. Personally, I've never noticed an effect when drinking tea. In the army we were allowed tea, but not coffe (we are not a tea drinking nation, so no bias involved here).

Do keep in mind that locals do drink a lot of super sweet tea... well, that's not entirely true, they spend a lot of time drinking it, with all sorts of tea sermonies and such, but not a whole lot actually gets drunk. Touaregs drink tea on their great camel treks. Good enough for them, good enough for me. Many herbal teas does not even contain teeine, but may contain other chemicals having a similar effect. There are also cleansing herbal teas (make you go to the bathromm big time) or teas that are designed to calm your nerves or to put you to sleep.

Stay away from alcohol

definately concur with much of the above, little and often is best, warm drinks are better than cold (some say you notice the heat more with cold drinks, maybe something to do with cooling the body core leading to peripheral vasodilation - who knows?). Extra salt in you water is uneccessary and too much salt will increase you dehydration and mess up you electrolyte balance. Isotonic saline (ie in tune with the bodies normal level) is just a 0.9% solution. don't forget your other electrolytes such as potassium (found in bananas), this is where sports drinks come in to their own. headaches are my first BIG indicator I am a bit dry, but individuals vary, some may only get headaches when seriously dehydrated.

As per my previous post, if you pee clear in extreme heat your drinking too much, incidently this is current British Army doctrine,. The pee clear thing was binned a couple of years ago after experience in the middle east, where soldiers were getting ill through drinking too much trying, aim for a pale orange. tea isn't as dehydrating as coffee or coke because of lower levels of cafeine (or whatever you want to call it) but it is still a poor rehydrate. I don't know what touareg tea is made of, but pg tips it aint! Personally drinking army tea always seemed to make me dehydrated, or maybe the green kit sucked moisture from me! it made me pee orange and it smelt like sugar puffs!! Try drinking half a dozen cups of tea in the morning (assuming your not used to it) and then see how much you pee! I would suggest the effect is a lot more pronounced than if you drank the equivalent in water. Drinking things like this can also misslead you, because it increases your diuresis (body's conversion of fluid) it will make you pee a lot clearer than you should be for your given state of hydration. That doesn't mean don't drink them (I am a tea-aholic), just be aware of the effect it has on YOUR body. what the locals do, in this case, isn't all that relevant. they have lived here all their life, and for generations before. their bodies are adapted, their metabolism is different, their clothing is different and they don't do daft things like ride bikes across the desert for fun (mad dogs and englishmen! (ok, and others!))

Andy