Besides not making that big of a difference in cooking time, Kenji Lopez-Alt explained that warm tap water often contains dissolved minerals picked up from your plumbing or hot water tank. These minerals can then go on to affect the delicate flavor of beverages like tea and coffee.
This bit of information came up during a discussion on the various myths surrounding boiling water, something that Lopez-Alt had been researching for his Food Lab column on Serious Eats. Besides the idea that cold water boils faster than hot (opposite what we believed, ironically), Lopez-Alt talked about salt making water boil hotter and how much alcohol cooks off during boiling.
His explanations of each myth and the reasoning behind them were very surprising!
• Hear the entire interview with Kenji Lopez-Alt: Boiling Water on KCRW’s Good Food