Just one small point for your consideration:

ORS formulae, such as that promulgated by the WHO, are intended for the treatment of life-threatening dehydration due to diarrheal diseases. It is not a treatment or prophylactic for heat illness.

A normal diet, in fact almost any reasonable diet, provides sufficient quantities of sodium and other electrolytes. In almost all cases, plain water in sufficient amounts at regular intervals, combined with perhaps smaller, more frequent meals and snacks, is sufficient to maintain proper hydration and electrolyte balance for healthy people, even in hot and humid environments.

However, while dehydration can, and often does, certainly contribute to heat illness, there is a level of exertion combined with environmental exposure that, regardless of fluid and electrolyte replacement or supplementation, will cause heat illness.

Just my $0.02.