Molgrips,
whisky is made in several stages – brewing to produce the alcohol, different strains of yeast and barley, and whether the barley was smoked and if so to what extent affect the final taste. distillation then produces the spirit, the shape of the still and spirit being reintroduced to the still (reflux) (I think the big thing here is how much copper the spirit is exposed to) . maturation then takes place in wooden barrels, some previously used to mature sherry (eg McAllan) others bourbon (eg Auchentoshan), sometimes it’s the first time the barrel’s been used, sometimes the the second, third or fourth. Sometimes the whisky is moved between barrels (Distillers editions) and sometimes a completely different type of barrel is used (Glenmorangie pioneer this sort of thing with things like Quinta Ruban (finished in port barrels) or LaSanta (Sauternes).
Water isn’t that big a part of the flavour variations of the end product.