hi,
i found the little bit of info i had read:
make your own 'isotonic drink': 500ml pure water, 500ml good quality fruit juice, 1/4 teaspoon salt.
it goes without saying on here, doesnt it, that 'fruit juice' means just that, not 'fruit juice drink' or cordials, squashes etc?
and i guess the person who wrote it decided, from all the 'waters' available (pond, toilet, swimming pool, bath . . ) that 'pure water' tastes best, tee hee hee!
good luck, and in the words of the very old NYPD Blues, be careful out there . . .
(showing my age now, no-one else needs to admit they can remember it too)