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Florestan
Since: May, 2015
2021-12-22 04:51:04
There's a related trope Kill It with Water, when contact with water causes someone to melt or disintegrate...
PCD
Since: May, 2021
2021-12-22 08:40:20
Heal It with Water exists, but doesn't fit your requirements of being disastrous. I'd use Kill It with Water because water causes a negative thing to occur.
Or maybe create a trope called Water Is Magical.

Before jumping to the line being from Gremlins, which I found out upon trying to look this up, hear me out please.
So in BoBoiBoy The Movie
(timestamp provided, yes the film's available on Youtube), the Tengkotak gang give Adu Du and Probe a task; to feed the alien squid Kurita, and not let it get wet. Probe questions how they'd get it wet - but are interrupted when the Tengkotak eject them into the ocean. Kurita turns into a Giant Squid as a result.
I recalled a similar line from a TAWOG episode, but it turns out to be a Shout-Out to a film called Gremlins, and looking over there, it's linked to their Explosive Breeder tendencies and, to a certain extent, Inevitably Broken Rule. So is there a specific trope for when contact with water causes something disastrous?