While I'd love to come up with some witty spiel about water and cocktails, I think the folks at Cooking Issues have done it here. The point is that shaking a cocktail with ice is more than just chilling it. If you were making a cocktail and put all the ingredients in the freezer and got it down to proper drinking temperature, it would taste off compared to those same ingredients shaken with ice. Water's dilution of alcoholic strength makes cocktails more palatable than drinking their component spirits straight.
Some popular cocktails containing Water
- Hulk Smash! — Bourbon, Bitters, Nin Jiom Pei Pa Koa, Lime, Water, Mint
- Himalaya — Cognac, Bitters, Mango juice, Lemon juice, Orgeat, Water
- Tipperary Cocktail (Dead Rabbit) — Irish whiskey, Sweet vermouth, Herbal liqueur, Orange bitters, Water, Simple syrup
- Hot Toddy — Scotch, Water, Demerara sugar, Lemon peel
- 5 Spot — Martinique Rum, Bitters, Lime juice, Water, Maple syrup, Ginger syrup, Basil