It only means. that the patient is encouraged if tollerated to increase his po or per mouth intake of water after having certain coniditons which lead to dehydration/ volume depletion in the first place.
Water + electrolytes. Generally drinking water is adequate for most with diarrhea to replace fluid losses. Drinks containing electrolytes and sugar may benefit some, especially infants and elderly, who could develop electrolyte disturbances from diarrhea. Pedialyte is a good example. Gatorade is another example but is generally thought to have too much sugar.