Daniel, Emily and Thalia are attending an athletic camp this summer. They were told they had to monitor the amount of water they drink daily. The first day, Daniel reported that he drank 1.9 liters of water, Emily said she drank 1,800 milliliters of water, and Thalia reported that she drank 7.5 cups. Which of them drank the most? Which drank the least? How do you know?