Use a combination of purified bottled water and directional freezing to create perfectly clear ice balls. Purified water has fewer impurities in it, allowing the water to freeze properly. Fewer impurities also reduce the chances of cracked ice balls once the liquid hits them. Cracked ice balls may increase the surface area of the ice, leading to faster melting and more dilution. Directional freezing pushes any impurities to one side of the ice ball rather than keeping them in the middle. Because ice freezes on the outside first and the inside last, the process pushes impurities to the middle. If there are any impurities in your water, directional freezing using a cooler within your freezer pushes any impurities to one side of the mold. When you create your ice ball using an ice ball press, the impurities automatically melt off because they are on the outside of the hexagonal ice mold.