really really cold lassi - made with a spoon or 2 of yoghurt, very cold water and/or chipped ice, tiny bit of salt, and (depending on your taste) a dash of cumin powder OR a little chopped mint OR a tiny teeny bit of sugar.
or gazpacho! OK, strictly speaking a food not a drink, but not too sugary and the most refreshing thing in the world. Liquidised salad basically - finely finely chopped red onion, garlic, tomato, green pepper, cucumber, little bit of olive oil, some more cold water (or icecubes, even better), salt, bit of extra passata or tomato puree if your tomatoes are anemic. you can chop all this by hand if you want to play with knives and get mad chef skillz, or just chuck it all in a blender and whizz to a pulp.
other than that I got nuthin', you've knocked all the obvious options out of the park already....