Cats can have watermelon, but only in moderation and with precautions. The flesh of the watermelon is safe for cats to eat and can provide hydration and some vitamins like vitamin C and potassium. However, cats should never eat the seeds or the rind, as seeds contain toxic cyanide and can be a choking hazard, and the rind can cause digestive issues and blockages. Watermelon is not highly nutritious for cats because they are obligate carnivores and their bodies are not designed to digest plant-based foods well. It should be given only occasionally as a treat, not as a regular food source, especially avoiding watermelon for kittens or cats with certain health conditions like diabetes. In summary, watermelon can be a safe and hydrating treat for healthy adult cats if seedless and rind-free, but it offers little nutritional benefit and carries some risks if not prepared properly.