In a medium-sized bowl, whisk garlic, olive oil, lemon juice, water, oregano, salt, and black pepper.
Pour into a large re-sealable plastic bag. Add swordfish and marinate in refrigerator for at least 2 hours, preferably overnight, turning bag occasionally to ensure even coating.
Cook on grill to medium-high heat. Cook until fish is cooked through and flakes easily with a fork. Approximately 4 minutes per side depending on thickness.