Cold water is the best option for hydration in the summer. The body is made up of 60% water (the bodies of children under 10 have up to 75%), and the hot weather causes it to lose a lot from perspiration. By the time you feel thirsty, you are already partially dehydrated. So during the hot months, make sure that you drink water every hour and give children water, too.
Children between 6 and 26 pounds (usually up to 2 years old) need between 3 and 6 cups of water a day (24 to 48 ounces), and children weighing 27 to 100 pounds (usually up to around 12 years old) need 4 to 8 glasses of water per day (32 to 64 ounces). Adults over 100 pounds need a minimum of 64 ounces of water a day and potentially more if a lot of the body's water is lost through perspiration. Extra water can also be obtained through any juice that you make. By adding twice the amount of recommended water to the concentrate, your body will receive double what it would have been getting through the beverage.
Sports drinks (commonly confused with, but not the same as energy drinks) are often considered one of the next best options for rehydration during the summer, since they not only provide the body with needed fluids but also restore lost electrolytes. They are designed to re-supply the body with carbohydrates, electrolytes and salts that it is using and losing while being active. After water, sports drinks are the best option on hot days.