CeeDee,
Try this; in addition CO2 discharges can creat a static discharge which can re-ignite a fire. Not very helpful when your last extinguisher is almost empty! In a confined space like a pax compartment in an A/C a large CO2 discharge will suffocate many of the pax.
As for water, not a goer as water and electrical cables/switch gear don't mix. Understand the Halon environmental case but still required in an A/C, find it difficult to understand why the EU have taken this line of action, no Engineers or Pilots amongst them!. Obviously none of them have had to put a fire out in a confined space. They want to attend some of the Fire Schools up here in Scotland, it would put the fear of God into them. In the offshore world all folk have fire fighting skills checked out every 4 years until they retire. No pass? No job!
Halon and its replacements(Larry Lippman, Mike Weihman, Urban Fredriksson)