In a small saucepan, bring sugar and water to a simmer. Remove from heat and add lime zest. Cool to room temperature, then cover and place in refrigerator to chill.
Place watermelon in a colander and mash with a potato masher or very clean hands. Allow juice to drain. You should have about 4 cups juice. Cover and chill.
When both items are cold, mix lime juice with sugar syrup. Strain the mixture through a fine meshed sieve while pouring into a pitcher. Pour watermelon juice into pitcher, also through the fine meshed sieve. Stir to combine. Pour over ice and garnish with watermelon wedges.