The MacAllan is wonderful stuff. I've a bottle of the 12, the 15 and the 25 sitting around here now. Ahhhhh...
As far as adding water.... at least to Scotch... lots of folks and Scotch distilleries advise that adding a few drops of water helps to bring out the taste and bouquet of a good whiskey. Adding water into the Scotch releases the esthers, which helps you experience the true essence of the Scotch.
I've tried it with all three of the MacAllans. Blind tasting with three good friends and longtime Scotch drinkers. Served each age separately with a tiny splash of water. We all preferred it with a bit of water.
YMMV.