How to find a water leak in my front yard???

If I have a leak somewhere in my front yard...I think...how do I find it? My water usage skyrocketed this past month and I have nothing to explain it. Also I can see the water draining from my front yard and running down the street. We have had a ton of rain so I thought it was just runoff, but now I cannot explain the water usage....How can I identify where the leak is? Is there a tool I can get to help narrow the leak in my front yard? Any help would be appreciated. Tim