A little lemon or lime juice is fine, also other fruits and veg you might like to make "spa water", e.g. Cucumber, orange slices, berries. Living in the American south now, unsweetened iced tea is always in my fridge. Southerners think it odd because it is not sweet, English friends think it just plain odd to have tea over ice, but it is refreshing anytime, including with meals, with or without the caffiene hit. Many herbal teas taste good over ice too, like the fruity ones, and leftover coffee. Anything on plan, is fair game to be put over ice in summer.