Determining Catchment Areas for rainfall

[Porklet]

EDIT: I wasn't sure where to begin this thread so I chose this forum. I hope I was right.

I am working on a world map. After reading several sources on the subject (including a thread started by Redrobes) I have decided to determine where the Catchment areas are located amongst the mountain chains on the map. I have never done this before. I worked on a few of the smaller chains, but I wanted to get some insight as to whether, or not, I am doing it correctly. I have included a WIP .jpg below:

The mountains themselves are merely representative at this scale, but I am using them as a guide for the water flow. Obviously, the catchment areas lie between any two pink lines on along the ridge line, or what have you.

Any feedback would be appreciated.