Since everyone drinks water, you know the liquid is most definitely going to be consumed when you give these bottles away. Water is also the perfect favor for hot outdoor weddings.
You can get bottled water from Costco for an affordable price or on Amazon, like this case of Kirkland Signature Premium Drinking Water ($30 for 80 8 oz. bottles). Slap on a customized sticker, and you're all set! You can get the custom water-bottle labels on Etsy ($45 for 100) or make your own using printable waterproof labels ($9 for 40).