Here’s a way you could do it with no plugins:
1. Create a solid white layer
2. Create a circle mask on the layer
3. duplicate the mask, set it to “subtract” and shrink it in slightly using the mask tools (not by scaling the mask)
4. This should give you a ring. Apply Fast Blur enough to make it fairly soft ( Fast Blur is the exact same algo as Gaussian blur, but much faster render).
5. Animate the scale of the layer from 0 – 200% or so, so you have a ring growing from the center out past the bounds of your screen.
6. Duplicate this layer several times, offsetting it in time for each by maybe 10 frames. This will give you a rippling waves type of look
7. Precomp all of these layers.
8. Apply Displacement Map to your footage, and use the precomped ripples as the source of the distortion. You will need to set the distortion to be based on Luminance rather than colors. Crank up the horizontal/vertical values to taste.
9. For extra credit, you could apply Compound Blur to the footage as well, using the same precomped ripples as the source of the blur. This would cause your footage to ripple AND have a slight blur as the ripples pass through it, which would look more like a heat wave than, say, a time/space distortion effect.