I've often heard that adding just a few drops of filtered, room termperature water to scotch helps to "bring out the flavor and the aroma." The scotch guy at my store told me it involves a chemical reaction; that barley is a tightly wound grain, and the water causes the molecules to unwind. Here's a slightly more technical explanation:
Nowadays just about everyone agrees that a little (emphasis on ‘little’) water helps a whisky (especially subtle or floral single malts) ‘open up’ in the glass. A chemical reaction occurs between the water and the tightly-wound chains of amino acids in the whisky. They literally unravel, releasing new flavor compounds and esters (volatile compounds that smell like flowers and fruits). How much water? I generally use a straw to pick up some water (you remember playing with fast-food straws as a kid, right?) and drop 4 or 5 drops into my glass. (source)
... place about a half-teaspoon of good quality, room temperature water in the single malt. I keep a bottle of such in my single malt cabinet. Now quickly swirl the contents a couple of times and nose again. If the whisky has much character, you will now most likely have to move your glass farther from your nose. There may be an intense release of aromas from the malt- or maybe not so intense. This robust release of aromas is due to the old Chemistry 104 term called "heat of solution." In effect, this rule states that when two chemicals are mixed, they may "take on" or "release" energy, thus becoming cooler or warmer. In the case of a whisky and water mix, the solution becomes slightly warmer, thus releasing the ethyl alcohols which contain much of the aroma of the single malt. (source)
Not knowing much about chemistry, I'm tempted to take anyone's word for it that invokes the old "Chemistry 104" rule. But is it really true?