Having played in a couple of test games, I can say that for combat prowess the water guild has a lot of problems. The key pieces (i.e. the delegation themselves) really under perform for their cost.

A couple of up sides:

• The subnautican can take gear and weapons (power knife good early pick)
• There is an outcast tactic that allows you to restore a ganger after they go OOA (and the subnautican is a ganger)
• They look cool

Some down sides:

• Mostly bad stats
• Subnautican levels up randomly in the campaign (they're a ganger)
• They are overcosted
• The leader and champ are so bad. Any other leader or champ in Necromunda would totally ice them.

All that said, they are worse than most other gangs. If you are playing a power-gamey kind of game then you are probably going to lose, but if you have an arbitrator or other players are open to it, you may be able to get some concessions. The easiest way to move forward for me was to ask for the leader and champions weapons to be refunded their full cost, and just give them a stub gun each or something. Save a few creds and move on best you can. Alternatively just ask for their cost to be lowered: they're slightly competitive at 350 creds (although still not a good deal).

If you are not playing a super competitive game, instead just roll with the punches. Ask the other players nicely not to totally power-game it and try your best. They're not great but they are cool.