Desiree Hartsock's Bachelorette 2013 has just begun! Since this question seems to come up several times every season of The Bachelor and Bachelorette, let's let the Rosemaster himself try to put it to rest.
As Chris Harrison wrote in his Entertainment Weekly blog for The BachelorSeason 16, Episode 2, "There is one thing I left out of my first blog I wanted to cover as it is always one of the most asked questions I ever get via twitter while the first episode airs. Yes, the driveway is wet. We water it down so that it looks pretty on TV. The other reason we water the driveway is we hope that someday it will grow to be a beautiful, big super highway."
So all of that water is not actually going to waste — it's a sacrifice on the altar of beauty.