Unless the cave collapses and/or the fight gets taken outside, Zabuza has no water source.
Zabuza can, however, activate his mist. Allowing Kakuzu to take off his masks for battle unharmed.
Kitsuchi anticipates Zabuza's attack, but not before Sasori fires off his senbon arm ( this is an AOE attack, and therefore it's a great counter to the mist ), and 1panels Zabuza and Kakuzu low diff

( let's not forget Kakuzu can't use Domu while deploying his masks since his body needs to move in order to do so )
If Kakuzu magically survives that, then he'll blast the entire cave with Katon/Fuuton and it's gg ( ._.)