Masks don't appear to have changed much over the years, I'd suggest keeping what you have in one clip rather than nesting everything and making more work than necessary.

If the drops and the surface they're splashing onto are constant, then you need only mask individually within the clips.

Do you have a dropbox account or other host for your .swf? When posting for help it's a bit more encouraging to see right away what stage you're at rather than downloading a zip and publishing the .fla