Japanese water stones are significantly softer than others. Some are made from natural rocks and are incredibly costly that only professionals prefer using them to sharpen knives. Because Japanese whetstones are softer, they wear down quicker. However, this also means more slurry is produced as you sharpen the blade. This enables Japanese whetstones to create a sharp edge swiftly. There are also Japanese oil stones, but the whetstones that require water as a lubricant are more prevalent.