"To Enhance Flavor, Just Add Water"

How can water reduce one sensation and amplify another? Both alcohol and aroma molecules are volatile, meaning they evaporate from foods and drinks and are carried by the air to the odor receptors high up in the nasal cavity.

Aroma molecules are also more chemically similar to alcohol molecules than they are to water, so they tend to cling to alcohol, and are quicker to evaporate out of a drink when there’s less alcohol to cling to.

This means that the more alcoholic a drink is, the more it cloisters its aroma molecules, and the less aroma it releases into the air. Add water and there’s less alcohol to irritate and burn, and more aroma release.

The same principle explains why stiff martinis and Manhattans can be less aromatic than lower-proof cocktails, as many bartenders know.

http://www.scotchmaltwhisky.co.uk/how-to-drink.htm wrote:ADDING WATER
Whether or not you should add water to your whisky is entirely about personal taste. Many who drink their whisky neat say they do not want to spoil the taste by adding water to it.

However, there are just as many whisky drinkers who say that adding a touch of water, especially soft still spring water will enhance the aroma and flavour of a whisky and bring out the whiskies hidden characteristics. It is worth noting that tap water can contain high levels chlorine and would spoil rather than complement your whisky, if this is the case with your tap water it is best avoided.

The true lover of whisky will drink their whisky as the professionals do, with a little clear water. Adding a little water to whisky before drinking will prevent the strength of the whisky numbing your senses and reducing your enjoyment of the whisky. It is widely said that you should dilute your whisky with a fifth water. Everyone's tastes varies, so its worth adding just a little water at a time to see what you prefer. Having said all that I do agree that some whiskies are best without any water added.