Psycho has elaborated it well...!

Drinking fluids is usually enough for mild dehydration. It is better to drink small amounts of fluid often (using a teaspoon or syringe for an infant or child), instead of trying to force large amounts of fluid at one time. Drinking too much fluid at once can bring on more vomiting.

Electrolyte solutions or freezer pops are very effective. These are available at pharmacies. Sports drinks contain a lot of sugar and can cause or worsen diarrhea. In infants and children, avoid using water as the primary replacement fluid.

Intravenous fluids and a hospital stay may be needed for moderate to severe dehydration. The health care provider will try to identify and then treat the cause of the dehydration.