Why do hospitals use saline solutions to hydrate patients instead of distilled water? ? need

Hospitals use saline solutions to hydrate patients instead of distilled water because saline solution has sodium as well as water. 
Sodium helps our muscles contract, sends nerve impulses throughout our bodies and regulates fluid balance so we don't become dehydrated. So, this allows for the patients that are dehydrated to replenish the salt lost from their body’s with the saline solution.

The salinity helps keep them happy and juiced up