In a medium sauce pan, whisk together the water, oil, vinegar, sugar, and salt. Over medium heat, bring to a boil. Off the heat and allow to cool to room temperature.
While the marinade is cooling, shred the cabbage and beets and transfer to a large mixing bowl. Add the garlic.
Pour the cooled marinade over the shredded salad and stir to combine. Press the salad down with a plate and weigh down with a bowl of water. Marinade overnight.
Drain and store in the refrigerator in a glass jar fitted with a lid.