RunnerPack has just released his impressive Water Ripple Demo for the Virtual Boy, featuring a realisticly simulated water surface. You should really see that in motion! I suggest you use the latest Reality Boy since it is currently not running correctly on hardware.
Left DPad: Create waves by moving an invisible cursor over the surface
Right DPad: Not used
A: Drop a small drop of water where the cursor is
B: Drop a large drop of water where the cursor is
L/R Trigger: Turn on/off higher brightness
Start: Pause (Water only, NOT cursor!)
Select: Let it rain!
Click on the screenshot to download the demo. It also includes the full source code! Discussion in this thread.