Whisk water, sugar, soy sauce, sesame oil, garlic, and ginger together in a large glass or ceramic bowl. Add beef short ribs and toss to evenly coat. Cover the bowl with plastic wrap and marinate in the refrigerator, 8 hours to overnight.
Preheat an outdoor grill for medium-high heat and lightly oil the grate. Remove short ribs from the marinade and discard marinade.
Cook short ribs on the grill until evenly browned, 3 to 4 minutes per side. An instant-read thermometer inserted into the center should read 145 degrees F (63 degrees C).