Water and proofing.
Whiskey or Aqua vitae is the "water of life," and the clear natural fresh liquid is vital to flavor. From the quality and source to the amount used for proofing affects how the whiskey tastes.
The source.
Water plays such a large role in the making of whiskey that proximity to water has always been important. The importance of water is why distilleries are set up next to local fresh spring water. It is why Kentucky distillers set up using natural limestone to filter water. Hell, it is why Arthur Guinness set up his brewery where he did. Many distilleries boast about their water source.
Proof and A.B.V.
Water is crucial in the role of proofing whiskey. When you add water, you change the A.B.V. (or proof), which changes the flavor. Taste a whiskey at 100 proof, then taste the same whiskey at 80 proof, and you will be surprised. Using water during the bottling process is not the only time distillers need to add water. Whiskey comes off the still no higher than 160 proof, but can not enter the barrel higher than 125. It has to get from 160 proof to 125 somehow, well water is the key. Water and alcohol evaporate from the barrel at different rates in different environments. So the proof the whiskey goes into the barrel is crucial to developing the final flavor profile. Distillers are experimenting with varying proofs of entry.
Water at home
The saying goes whiskey neat tells you the truth, but whiskey and water will tell you its secrets. Add a few drops to your whiskey, and it will open up. Technically it is changing the amount of alcohol in the glass. Chuck Cowdery has the formula to help you get the exact proof you want.
(amount of whiskey) x ((bottle proof/desired proof) -1) = amount of water to add.
2 oz whiskey x ((100proof/90proof)-1)= 0.22 oz of water
Next time you pour a glass of your favorite whiskey, try it neat next to a version with a touch of water. Do you taste the difference? Which do you like better? It might be different with each whiskey. Water plays an essential role in whiskey and its flavor, so don’t overlook this simple ingredient.