Before you even ask, beer and wine don't count toward keeping you hydrated. If your outdoor wedding day is forecasted to be a scorcher, be sure to supply extra bottles of water and other hydrating beverages to keep your guests in tip-top condition. You want guests to remember your wedding as a magical day -- not the day they spent thousands of dollars on an ambulance ride to the hospital as a victim of heatstroke.
Play it safe and encourage guests to enjoy a variety of libations, including the nonalcoholic kind. Ask your mother or wedding planner to keep a special eye on tykes and elderly people in attendance; these groups are more apt to become quickly dehydrated.