Health We Asked Experts Whether Drinking Days-Old Water Is Dangerous, And Their Answer Was Surprising Many of us chug leftover water without issues, but there is actually a tipping point when it’s better for your health to dump it. I regularly drink from stray glasses of water I see scattered around my house that were poured the day before. I think I’m being efficient and resourceful, but am I being safe? Experts say there is actually a tipping point at which it is better for your health to dump that glass of water and start afresh. Kristen Smith , a dietitian and spokeswoman for the Academy of Nutrition and Dietetics , said that she personally follows a 12-hour rule for a glass of water. After 12 hours, Smith will pour it out and drink a new glass. However, she said you can drink a day-old glass of water “as long as it hasn’t been exposed to contaminants or left uncovered.” Microbiologist Jason Tetro, aka “The Germ Guy,” also said 12 hours was the limit for drinking leftover water in glasses.…