Dark colored bottles (i.e. black, purple, dark blue,etc.) are known to help preserve your alkaline water! The dark color acts as a UV protectant and helps preserve and store your ionized water! Bisphenol (BPA) is a chemical produced in large quantities for use primarily in the production of polycarbonate plastics and epoxy resins. These custom water bottles will allow you to quench your thirst while using bottles that are free of chemicals. These bottles contain Tritan material, which is believed to be one of the safest alternatives to BPA for manufacturing water bottles. Tritan is the brand name for copolyester, a tough BPA-free material that has similar properties to common plastics such as polycarbonate. Tritan has chemical resistance and maintains its integrity in environments where other materials may degrade.