Make the raspberry syrup:
Puree the raspberries in a blender with ½ cup water then add it to a medium saucepan with the sugar. Bring it to a boil over medium/high heat, then reduce the heat to low and simmer until the sugar is completely dissolved, about 5 more minutes. Skim any foam that's accumulated on the surface of the syrup. Remove from heat and allow the mixture to come to room temperature. Strain to remove the seeds and set aside until ready to use.
Make the berry puree:
To a blender, add the strawberries, blueberries, and water. Blend on high until completely smooth. Strain to remove the solids. Allow to stand for five minutes and skim off any foam that's accumulated on the surface of the puree. Set aside until ready to use.
Make the sangria:
In a large pitcher (One that holds about 2 gallons) add the raspberry simple syrup, berry puree, lemon juice, berry vodka, Moscato, blueberries, strawberries, raspberries, and lemon slices. Stir to combine, or if you’re using a container with a lid – Shake it! Cover and place in the refrigerator for at least an hour to allow the flavors to meld and that situation to chill.
Serve topped with seltzer.