Fun!

My uncle engineers water reservoirs and a few months ago he took me on a tour of a 45 MegaLiter concrete subterranean reservoir he had engineered. They were in the process of fixing a leak they discovered - using Kool-aid.

After discovering the leak, they gave a scuba diver a flashlight and a plastic bottle filled with bright red Kool-aid powder. The diver squirted the powder at various places around the reservoir and paid attention to where the red dye went, which found the leaks.