If you are working with pure ethanol then it is an easy task - circulating the tank with a pump-around or agitating with a paddle will quickly get the mixture homogeneous.
But if you are blending potable spirits it is a different matter. Never add the whisky (or whiskey, depending where you live) to the water - always add the water to the whisky. And never mix them while hot. Both of these mistakes will result in a cloudy blend.
The reason for adding alcohol first to a drink glass is that alcohol is lower density than water or other ingredients. If you add it last, it will float without mixing unless stirred (or shaken). If you add it first it will mix much better. Do not just pour the additives in one spot or they will channel to the bottom of the glass as the alcohol floats up. Pour around the surface. Ice in the glass helps when mixing this way. Professional bartenders rarely stir drinks.
By inline mixing I assume you mean you simply pump the water and alcohol into the same line.
Not good enough, I recall reading a report on a water line which carried water from two different sources, identifiable through analysis, and they found the two streams were flowing as separate parralel streams in the pipe for some considerable distance.
You have two low viscosity fluids here so adding a static mixer into the line wouldn't create too big a headloss penalty. Search for static mixers or Vortab, Chemineer, etc.
