Buying a watermelon can be annoying. Citrullus lanatus is essentially a gigantic ball of water due to its 92% moisture content.
They're tasty and full of vitamin C and D, so they'll keep you from getting scurvy.
What's the best way to choose? Kitchn's Emma Christensen recommended weight training. In the vegetable section of your local grocery store, look for the heaviest watermelon for its size.
Juice is higher in denser fruits. That's when it's ripe. Find the "splotch" on the watermelon's underside. The watermelon's yellow spot comes from sitting on the ground.
If it's creamy yellow, it's ripe too.
Finally, smack the underside to check for hollowness without drawing attention from grocery workers.
Good if it does. If it sounds dull, like hitting a solid brick, it's overripe. Put the watermelon down and carefully back away from it.
There's another way to evaluate watermelons if you're not sure: Any watermelon you buy at a local farmers market is likely to be good.
The vendor can also choose one for you. When you have to pick your own produce, watch him and try to copy him.