To a medium saucepan over medium-high heat, add the water, sugar, and ground cinnamon. Stir to combine. Cook until the sugar is dissolved. Remove from heat and set aside.
In a 1.5-gallon (or larger) punch bowl whisk together pumpkin puree, apple cider, spiced rum, vodka, seltzer water, orange juice, and lemon juice. (Using a whisk helps break up the pumpkin puree.) Pour in the cinnamon simple syrup and stir everything together.
Add lemon slices and a few cinnamon sticks to the punch bowl. Chill until ready to serve.
Portion punch into punch glasses and garnish with a cinnamon stick, if desired. You can fill the glasses with ice first, or not depending on your preference.
This recipe makes 1 gallon of punch which yields sixteen 8-ounce servings.
To make this post non-alcoholic, substitute 3 more cups of cider, 1 cup of orange juice, and 1/4 cup lemon juice for the booze.