Tap on the watermelon and listen to the sound. If the pitch sounds deep and hollow, the fruit has more water and is likely riper.
Dry weathering spots and vein-like webbing lines are great indicators of sweet watermelons.
Look for a round and more evenly shaped watermelon instead of an oval one as they are sweeter in taste.
Pick a watermelon that has a strong and consistent stripe pattern. The stripes should be dark and dull-looking.
While picking a watermelon, inspect its stem. Make sure it is dry and yellow-brown in colour.
The best time to buy a watermelon is between May and September.