Add the frozen berries, vodka, sweetener, and water into the blender.
Secure the lid and blend on high speed until the mixture is smooth and has a slushy, semi-frozen consistency, about 30-45 seconds.
Check the texture; if it’s too thick, add a splash more water and blend briefly to loosen it up. If it’s too thin, add a few more frozen berries and blend again.
Once blended to your desired slushy texture, pour the mixture into chilled glasses.
Garnish with a fresh berry or a slice of citrus if desired, and serve immediately to enjoy the icy chill.