Iran's capital Tehran is counting down to "day zero" - the day the water runs out and the taps run dry. Reservoirs that supply Tehran's 15 million residents are almost empty. President Masoud Pezeshkian has urged people to use water sparingly - or the city, or at least parts of it, may have to evacuate. Sky's science correspondent Thomas Moore looks into how Iran is trying to avoid disaster. Read more: https://news.sky.com/story/the-countdown-to-day-zero-major-city-may-have-to-evacuate-as-water-