I'm trying to use a Dowsing Rod to find water and (given you guys are the only ones I've seen so far), decided I should verify information to update the Wiki page. Here's what I've noticed:
1) Dowsing rod radar goes off about once every 30s. This makes finding water long and tedious.
2) The direction the pie slice is facing will change periodically. Perhaps it points towards the water?
3) Pie slice shrinks as you get closer to the water (given from the wiki).