If you follow the golden rule of watermelon prep — cutting just the amount you need — you will likely need to store a larger piece of cut watermelon, in addition to all the bite-sized pieces that were cut up. Here's the best way to do it.
For Large Pieces of Cut Watermelon
The best way to store any piece of cut melon, regardless of the size, is wrapping the cut end with plastic wrap and storing it in the refrigerator for up to a week. The role of the plastic is two-fold: It prevents the melon from picking up any odors or flavors from other foods in the fridge, and it keeps the fruit's flesh moist.
For Bite-Sized Watermelon Pieces
Once watermelon is cut and cubed, store anything you're not eating right away in an airtight container in the refrigerator. Cut watermelon pieces are at their best when eaten within three to four days of being cut. Soon after being cut, the liquid slowly seeps out of the flesh, and along with it, the sweet flavor you associate with watermelon.
For Long-Term Storage
If you have more melon that you'll eat within five days to a week, your best bet is to store the cut melon in the freezer. Remove the rind, cut the melon into pieces, and then freeze in a single layer on a baking sheet until solid. Store in an airtight container or zip-top freezer bag for up to six months.