You have to be cruel to be kind.
Your lens is letting you down, I'd guess it's a kit lens that came with the camera. If he is half serious have a look at the sigma ex series 70-200 f2.8 nice lens for the price specially if you can get a 2x convertor. If you really love your son canon L series.
Don't shoot program mode, the camera is stupid. You have to make a decision on what you want, is the depth of field (aperture) important or the speed.
Shoot manual, you need to be in control.
Buy a grey card and use that to set your exposures manually, or expose on the white water and over expose by 1 to 2 stops. I find shooting digital you have to go 1 stop over to get a bit of punch into the shoot, over film (he can google what that is

).
You can use the info button at the back to see the exposure curve, it should be a triangle shape, or similar, with the end of the shape at the far right.
Rule of thumb: Sunny 16 rule for exposure to get you in the right ball park then adjust from there.
The shutter speed was slow on some shots hence the out of focus or blurred looked. Also because its in a program mode the camera is trying to get the correct exposure, so check the ISO of the photos and see if they vary around. The higher the ISO the grainier the shot. If it's like over ISO400 you don't have enough light.
Focus manually sometimes the spray throws the auto focus out, especially that far out.
Keep an eye on the horizon to keep it straight, the idea is to limit the post production work.
Post production cropping - cropping too much also pixelates the final image, try not to go below an image size of 2848x1898 if you want A3 prints
I need to stop know, too much info. Most of all practice the settings at home, line up a 5 or 6 bottles one behind each other, put the camera on a tripod and change the settings to see how the image changes.
Don't be one of those photogs that shoots a 1000 imagines and hopes for the best, try to make each one count. I watched a doco on this professional wildlife photog and he shoot 500 rolls of 36 film and only got 6 good shoots, now that's picky.
Enjoy