Having a friend that was the founder of the LA Scotch Club has many advantages. One of them was access to enough variety of Scotch to properly determine how much water to use. For a dram of normal 40-46% Scotch, just a tiny drizzle is all you need. Like if you can't count how many drops went it you probably used too much. For cask strength (50-58%) I would use a little more, but not much.
Those small amounts of water are enough to produce the heat of mixing and release some of the finer aromatics. But too much water would result in that heat being absorbed by the water more than the whisky and therefore not releasing those aromatics as well, plus dilutes the whisky too much.
