I dunno- loose balls with grease work pretty darn well for me- less friction and longer lasting than cartridge BB's. If your BB shell is threaded crookedly, then you may not be able to put in a cartridge BB unless you get it rethreaded, and even then you may not have enough good threads left. So, for water intruson in a cup-and-cone, I'd do two things:

1) Drill a hole in the bottom of the BB shell to let the water drain
2) Put in one of those accordian-like plastic shields that isolates the BB bearings

Check it and regrease it periodically, and you're good to go...