The cooling water never touches the spirit — so why does its temperature change the whisky?
Condenser water sits on the far side of a copper wall and never meets a drop of distillate. It is also the largest water stream on a distillery site, and its temperature is one of the few flavour levers a distiller can move without changing anything else. Warmer water condenses vapour more slowly, slow condensing means more copper contact, and more copper contact means a lighter spirit.