The science is there. It is likely that Kolar's lightsaber would malfunction if submerged. However, I'm still doubting the ability for Fisto to break the plumbing without a good deal of concentration. I won't say that it's impossible because, let's face it, bigger things have been done.
Technically all it would take is a good saber slash from Fisto's saber (which can operate underwater), then he can manipulate water all he wants. All it would take is an instant, if he can get access to a lot of water Kolar loses, because Fisto would have an operating weapon while Kolar would not.