Apparently, it was only about a year ago that scientists discovered how insects (water skimmers) walk on water; they’re not heavy enough to break the surface tension of water. Water striders move by pushing down on the surface of water enough to create valleys but not enough to break the surface. The water then bounces back like a trampoline to push the insect forward.
Now scientists have created a robot that walks on water: "With inspiration from nature and some help from research at the Massachusetts Institute of Technology, a research team led by Carnegie Mellon engineering assistant professor Metin Sitti has built a tiny robot that can walk on water, much like insects known as water skimmers, water skaters, pond skaters or Jesus bugs." See this AP story.