Combine lemon juice and sugar in a large container or pitcher. Stir and let sit for 5-10 minutes, stirring every so often, until the sugar is fully dissolved.
1 cup lemon juice, ¾ cup sugar
Cut watermelon into chunks and place in a blender. Puree until smooth.
6 cups watermelon
Pour pureed watermelon into a fine-meshed sieve over a large bowl to strain off the juice. You should have about 3 cups of juice.
Pour watermelon juice and cold water into the pitcher with the lemon juice. Stir to combine.
4 cups cold water
Serve with ice. Refrigerate watermelon lemonade and use within 3-4 days. Stir before pouring.
Notes
If using a seeded watermelon, remove the black seeds before blending.
This lemonade is on the tart side. If you prefer a sweeter lemonade, add ¼ cup more sugar.
Make certain the sugar is completely dissolved in the lemon juice before adding the other ingredients. This will take 5-10 minutes.
If you're short on time, you can dissolve the sugar in a cup of water in a pan on the stove over medium heat. Remove as soon as the sugar has dissolved. Add to a pitcher and then add cold water. Finally, add your juices.
This lemonade separates as it sits. Just stir before pouring.
If adding ice to the pitcher of lemonade, reduce the amount of water added by ½ cup. This helps prevent the lemonade from becoming watered down.