With a large, sharp knife, remove the top 1/4 section of the watermelon. With a melon baller, scoop flesh from inside of watermelon, removing as many seeds as possible. Leave 1 cm of flesh inside the shell of the watermelon. Scoop cantaloupe and honeydew in the same manner, removing as much flesh as possible and discarding the rinds. Refrigerate fruits separately until ready to assemble.
In a small saucepan over medium-high heat bring water and sugar to a boil. Remove from heat and continue stirring until sugar has completely dissolved. Add lemon zest and set aside to cool.
To serve, place watermelon balls, cantaloupe, honeydew, oranges, pineapple, strawberries and grapes in a large mixing bowl. Pour syrup over and toss thoroughly. Transfer mixture to watermelon bowl and serve. Set aside any fruit mixture that will not fit. There will be enough fruit to refill the bowl.