Cucumbers are 96% water, making them an excellent way to boost your hydration. Yet, compared to other water-rich fruits and veggies, such as watermelon, celery, and tomatoes, cucumbers have fewer calories, adding to cucumber health benefits. Cucumbers are 96% water, making them an excellent way to boost your hydration. Yet, compared to other water-rich fruits and veggies, such as watermelon, celery, and tomatoes, cucumbers have fewer calories, adding to cucumber health benefits.