AFAIK, there is no mod to remove the water chip quest time limit and as it's so integral part of the game I doubt anyone interested in trying to remove it. It's quite genereous (150 days extendable to 250 days) and after completing it you have 13 game years (from start of the game) to complete the game (I believe this is game engine limit and simply causes automatic game over if you reach it).

Oh and you probably don't want to install TeamX's Fallout 1 Restoration project as it restores the 500 day time limit (down to 400 if you reveal the vault location to anyone) and the mutant invasion in full force and cities will start to be wiped out as early as around 90 days into the game :-p.