How much water to reach your target ABV.
The dilution formula is: Water = (Current Volume × Current ABV / Target ABV) - Current Volume. When mixing alcohol and water, a slight volume contraction occurs (~3-4% for spirits) due to hydrogen bonding between ethanol and water molecules. For precise results, distillers use the Gauging Manual tables. Always add water to alcohol (not the reverse) and use distilled or deionized water to avoid off-flavors from minerals. After dilution, let the mixture rest 24 hours for complete integration. US proof is simply 2× ABV (80 proof = 40% ABV). Most spirits are distilled at 60-80% ABV and diluted to bottling strength of 40-50%.