One cup of orange juice (249g) contains almost 90% water (219g). It also has 20.8g of sugar, which is almost equal to women's recommended daily sugar intake (25g) and half of men's (36g), which is why it's not recommended to drink more than one cup a day.  Even though drinking orange juice is healthy in moderate amounts, it doesn't replace water. To stay hydrated, drink a gallon of water every day.