Yes, running in water is great for building up power. I think the Mohammed Ali reference was more directed to Mohammed Ali throwing punches underwater, which is better than using weights. If you think about punching with weights for example (also with running but same idea) we see that gravity takes the arm only one diredtion. Underwater, you feel resistance from not only moving foward, but backward and to all other sides. It's quite wonderful.
And running in sand is equally great. The sand absorbs the impact and therefore requires you to output more energy to go. And running barefoot is really invigorating.
Ahhhh, I'm smiling right now. Hahahahha!