When you have a fever, you should drink more water and eat more fresh vegetables and fruits. Watermelon contains more water, so you can eat more when you have a fever. Watermelon is known for its heat-clearing effect. Eating watermelon can promote urination, and when you urinate, you will bring some of the heat out of your body, which can help cool down your temperature. If you have stomach pain or bloating or diarrhea when you have a fever, it is best not to eat watermelon. Because watermelon is cold, eating too much of it may cause diarrhea and other conditions. So it’s best to drink more warm water when you have a fever, and if you don’t have digestive symptoms, eating watermelon can help cool you down.