When purchasing Potassium Alum (Potassium Aluminum Sulfate), you must prioritize purity levels, typically ranging from 99% to 99.5% for industrial or food-grade applications. Pay close attention to the physical form, as it is available in lumps, granules, or fine powder depending on your specific use case. For water treatment, solubility rates are critical, while for cosmetic or food applications, you must ensure heavy metal content (such as Lead or Arsenic) is within strictly defined safety limits.