Puree sour cream, basil, mint, scallion, and water in a blender. Add cucumber. Pulse until just combined but still slightly chunky.
Stir in lemon juice and hot sauce, and season with salt. Chill soup at least 3 hours (soup is best served the same day). Top each serving with thin cucumber slices if desired.
This soup is very easy and fast to prepare, delicious and refreshing. I made it using natural yogurt instead of sour cream, as iI felt sour cream would make the soup too heavy, especially in hot weather. I added a couple of tablespoons of cr?