I hire in (or borrow) cameras so it's not that easy for me. And I'm not too convinced that it would be an easy thing to shoot and get right. I've done a fair number shoots involving water. They're fun, but really tricky.

So what would I be capturing? Some sheen and reflected highlights in order to overlay them later. Some of the highlights should concide with the texture in the jpg - a crack should glisten along one edge, etc or it would look like it's floating on top. The light would have to be from the same angle. The amount of trickle has to be convincing. If it's supposed to look like a six foot high concrete wall (like the jpg does) then there are probs with the water possibly trickling too fast or looking too 'big'. Could lay the cardboard at an angle to slow it down, but even then it may not scale up convincingly. To actually see the water's texture it would have to be sidelit, which conflicts with the rest of the composition (but maybe that's ok). Lit from the front it would reflect the source light nicely, but just look wet. Maybe too wet.

The more i think about it the more difficult it seems...

That motiongraphicslab example is very nice and worth taking a note of for use elsewhere, but here it would look like the wall was at the bottom of a pool!

Cheers though guys!

p.s. Here's a very similar concrete wall: <http://www.harefort.com/portfolio/wall_concrete01.jpg>