another thing to help hydrate you is to drink things like powerade, gatorade - your body doesn't always take up water all that well...

i can't stand the flavour of those sorts of drinks, so really weak cordial, or diluted fruit juice are also good for hydrating you.

i've found my best friend lately for countering dehydration has been fruit juice icy poles. berri quelch tube icy poles are 99% fruit juice and taste pretty good. and when MS does hit, they give you a sugar hit to stop the nausea a little while you get something more substantial into you... i can sorta get just over two hours without food, then i'm in trouble - but if i have to go longer, i hit that two hour point and have myself an icypole and i get an extra half hour or so....