Many vodka producers make a big deal about the source of the water used in their products. There are claims of glacial water sources, deep well water, water from exotic locations, etc. But really, how important is the water that is used in making vodka?
When making our vodka, we introduce water directly in our process (as opposed to water used for heating and cooling that never comes in contact with the product) at three different points. First is the water used for creating our mash (see Mashing). Second is water we add back to produced alcohol before the final distillation. In both cases, this water ends up being distilled, so, although we use clean water to begin with, if there were any impurities they would be cleaned up. The third point in the process where water is introduced is the most significant; the addition of water to dilute the 95% alcohol produced to 40% alcohol for the final product. For any vodka producer, the water used for dilution is the water that is most important to the quality of the finished product.
For our Single Malt Vodka, we use only three ingredients: malted barley, yeast and water. Other producers might use a different type of grain (e.g. wheat or corn), a combination of grains, or more rarely potatoes, beets or some other natural source of sugar. The yeast may play a role in determining the vodka character, but its effect on taste and aroma are probably negligible. Some vodka producers may also add other ingredients to their product, such as glycerin (see Does Grey Goose Contain Glycerine?) which most definitely does affect the taste and aroma of the vodka. The processes used to distill and the unique techniques from one distiller to another also play a role. We feel that the grain contributes the most character to our vodka, as it does for most vodkas we have tried. As a result, we don't want the water we use to affect the taste of our product. Our desire is for the water to be as neutral as possible.
Even if other producers use water from unique sources, there is good reason for them to treat their water first. Water, whether from municipal sources, natural sources or from some exotic origin, will surely contain impurities. Water is often very rich in minerals. However, alcohol reduces the solubility of minerals as does temperature (and most people enjoy their vodka chilled). Therefore, mineral rich water, regardless of its source, will become cloudy when added to alcohol. This may also cause precipitate to form in the bottle, especially at low temperature. Most of us will agree that a cloudy looking vodka is undesirable, and thus the need to use "soft water", removing impurities from the original water.
The process used by Still Waters Distillery involves a combination of carbon filtering the water, softening the water, and using reverse osmosis. We remove chlorine, chloramines, fluoride, etc. as well as the minerals in the water. Thus, the water we add to our vodka to dilute it is very pure and clean. (We also chill-filter the final product after dilution and before bottling.)
We don't believe that the water we use imparts any flavour to our vodka. We also believe that this is true for most producers, out of necessity. I would be much more concerned with the other ingredients used by distillers and the processes and techniques they use to distill their products.