What's the best drink for seniors to cool down in the hot summer days?

My friend from Thailand said they always drank hibiscus tea from morning till evening when it got really hot there and it cooled them down. I have researched it a bit and it also lowers blood-pressure and cholesterol levels, so that makes it even better for me. Know any other good drinks for summer?
Update: I am very surprised no one has mentioned watermelon juice, easy to make...just put chunks of watermelon in a blender with ice cubes and blend. The seeds drop to the bottom of the drink. I also make cantaloupe juice. Both those fruits are very refreshing.
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