As for water ripples (specifically), any point light source (need not be a projector - some LEDs would work well), a (clear) tank of water, and a ripple generator of some sort. We used to do this with overhead projectors and a 12x12x1 inch tank to illustrate waves in physics classes. Bounce off mirrors if you need it anywhere other than under the projector, gravity is uncompromising when it comes to water.