Diageo Plc, the world’s biggest spirits company, is worried that climate change is going to make scarce the one ingredient that’s essential for making all of its alcoholic drinks: water. Water security poses the most significant climate change-related risk for the maker of Tanqueray gin, Guinness beer, and Baileys Irish Cream, according to Michael Alexander, global head of water, environment, and agriculture sustainability at Diageo, which had 43 sites globally in water-stressed areas last year. “You could be with the most efficient brewery or distillery in the world,” Alexander said in an interview.