Watur, designed by Daniel Harper, is an actual door made of constantly flowing water. I'm not sure how secure a water door is, but it looks funky. It consists of a frame with a catch basin at the bottom to catch the falling water. Custom sizing is available and will cost around $2000.
Implications - Although $2,000 might seem like a lot of money to spend on a door, you really can't get much more creative than a portal in your home that consists of falling water. As far as conversation pieces go, this one is really high up there on the list. It's hard to imagine that any guest to your home would be able to resist the urge to test this awesome product out at least once.