The quickest way to annoy a Scot is to take an expensive single malt whisky and add ice and a mixer. It's considered a sacrilege. Single malts are enjoyed like wines for the infinite variety of flavors that come from the water, the grain, the stills and the barrels used for aging.
That having been said, adding water can actually open up the flavors of the whisky. How much water? Up to you. Serious tasters may add only a couple of drops. Casual enjoyers as much as one-third water. It’s all about personal taste. Experiment and enjoy. The kind of water is important for tasting. Tap water can ruin the flavor a good whisky. Use bottled water or water that has been boiled to give your drink a neutral canvas to play on.
Ice is another matter. It can actually stifle the flavor of a whisky. But sometimes you just want a cool drink. So go for it. Whisky stones have become popular lately as they chill your drink moderately without diluting it. They are available on-line and at most liquor stores.
If you want to experiment with flavor changes, freeze some distilled water in an ice cube tray, then add a cube to your whisky and see how the flavor changes as the ice melts.
So grab a glass and let's go!