An old classic:
According to him when you add water you're looking to get your scotch down to ~35% ABV.
Was interesting to see this thread bumped as I just read an article about budget scotches a couple of hours ago. Take it for what it's worth, as I haven't tried any of the scotches on the list so I can't say whether the author is full of crap or not.
http://www.seriouseats.com/2014/10/b...pigs-nose.html