Better than water,
add 1tsp/litre salt and 4-5tsp/litre sugar to water or dilute orange juice, to make up for the salts and sugars lost and stop cramping and things - it's the imbalance of ions as well as the dehydration that kills people with diarrhoea and vomiting if it goes on too long.

That, or have some sachets of dioralyte in the medicine cabinet. Tastes horrible, but makes you feel a bit better if you can keep it down.

Apparently children's wards in hospitals use flat coca-cola too, if the kids can't keep anything else down, though I've never tried that myself.
(epinephrine, Thu 29 Jul 2010, 23:03, 2 replies)

Flat cola works a treat.
My father used to work in the jungle an awful lot, and said the best thing for rehydrating his students is flat coke: it's less likely to induce nausea, and has a good amount of sugar in it. Adding a pinch of salt is also a good idea. They used to use Gatorade, but that tastes like syphilitic piss and makes me hurl.
(The Empress it seems you CAN polish a turd!, Fri 30 Jul 2010, 10:37, closed)

Powerade
Blue or red, your choice, but it's the absolute bollocks for rehydrating. Doesn't do much for salt levels, I grant you, but a hell of a lot better than water.
(bblgoose, Fri 30 Jul 2010, 10:45, closed)