I have never had a tank leak on me, and some of my tanks are ten years old. All I have are glass tanks.
Is this 30 gallon new or used? Either way, you can fill it up with freshwater first and let it sit for a day or two to make sure there are no leaks before you set it up. But I would be very very shocked if you had a leaky new tank.
Water damage depends on how much water comes out and what it falls on! Even though I have never had a tank leak, I have drained water on the floor when I wasn't carefull. One time on a freshwater tank I had an airpump sitting down low. I unplugged it and forgot about it and the water slowly back siphoned out of the tank, all over the carpet. We didn't realize what was going on until we felt the squishy floor. Lots of towels, open windows, and a box fan fixed everything right up. Never had equipment fail and cause a flood though, always been user error.
When I set the tank up in an area where there is carpet, I always put something in between the stand and the floor to catch drips. We recently re set up my 155, after having installed brand new carpet. 8O I got a piece of wood that was about two feet wider than the stand, front and sides, and flush with the wall in back. I even stained it to match the stand. This way, the inevitable splashes fall on something easy to clean.
