You don't really care about the details, do you? 

Technically, it's a non-newtonian fluid called oobleck (no, not that oobleck), so maybe it's not the exact same thing as water, but still it's pretty impressive. Another kind of non-newtonian fluid is silly putty, if that helps give you a better idea.

This oobleck pool seems like a cool thing to have in your backyard. It's an instant party-starter. "Hey, you guys wanna come over? Yeah, we can do some grilling, maybe a little oobleck-walking. You know, just a regular Saturday afternoon. Okay, later."