It was raining the other day, and after driving through the sixth or seventh puddle, my belt slipped off. Eventually pulled over, slipped it back on, and continued with my day.

Is this any sign of trouble, or just normal puddle antics?

Get the tensioner wet and there'* nothing to hold the belt in place. It will just walk right off the pulley. Under load makes it more likely.

Just making sure. I noticed a couple of new one-star reviews of my new belt tensioner on Advance'* site.