Roots need water, but they need air too! Watermelons especially don't like wet feet for too long. How often you'll need to water will depend on your climate and soil type. I'm in the lower Mississippi delta, with very sandy soil, so there are times in June and July when I really do have to water daily to keep things alive. My friends a mile down the road have a lot of clay in their soil, so during those same months they may only water twice a week.
If you're unsure when to water, dig a small hole in the dirt near your plants with your finger. If the soil an inch below the surface feels even slightly moist, your plants are fine. You only need to turn on that soaker if your soil is starting to get dry and dusty.
