RLW, here's a chemistry/physics bit for you to mull over (this info can be found in books on the topic):
the chill has is usaully the result of carbonates, either calcium or magnesium carbonate. I'm not sure exactly where it comes from in the process, I'm still learning this stuff myself. In high proof alcohol, carbonates have very high solubility, so it will be crystal clear. However, when you add water, this reduces the abv, dramatically reducing the solubility. So instead of being in solution, the calcium or magnesium ions get together with their carbonate brothers to form the full non-dissolved carbonate molecule - hence, haze. Temperature affects solubility (think about the difference between stirring sugar in to cold water versus a cup of hot tea - the hot tea dissolves the sugar almost instantaneously and can accomodate much more than cold water). This is why people refer to chill filtering. Make your vodka as cold as possible so as much of the carbonate precipitates, and then filter. This removes as much carbonate as possible from the product.
In the small amount of experimenting I've done, I've been surprised to see how much carbonate makes it's way through the distilling process. Starting with soft water seems to be the way to go, as long as it doesn't adversely affect your yeast. That being said, I believe calcium is a vital yeast neutrient.
Cheers,
Dave
