Water is essential for all body functions. Digestion is impossible without it. Walking in hot weather or where there is excessive fluid loss through perspiration requires not only adequate fluid intake but also electrolyte replacement (sodium, potassium) to offset dehydration. Saline powder or salt/glucose should be taken in balance with water. The formula recommended is 2 g salt, 50 to a maximum of 100 g glucose in one litre of water, plus flavouring to mask the salty taste. An alternative is a formulated electrolyte replacer (e.g. Staminade, Gatorade (powder) or Vigorade (liquid)). In the specified mix with water there is almost instantaneous absorption into the body.