Add the cantaloupe, water, and sugar into a large blender. Blend for 1 to 2 minutes until smooth. You may have to do this in batches if your blender isn't big enough.
Taste and blend in more sugar if desired. Strain the mixture into a pitcher to remove any pulp.
Serve immediately over ice or chill in the refrigerator for up to 3 days.
Notes
You can adjust the amount of sugar based on the ripeness of your cantaloupe or to your liking. For a less sweet agua fresca, only use half of the sugar.
If you like pulp, you can omit straining the mixture.
Garnish with diced cantaloupe, or add a squeeze of lime juice for a citrusy twist.