Whisk the base. In a bowl or jar, combine the water, vinegar, lemon juice, olive oil, sugar, and salt. Whisk until the sugar and salt dissolve.
Add the seasonings. Stir in the black pepper, dill seed, crushed rosemary, lemon zest, garlic, onion powder, and citric acid.
Thicken (optional). For a bottle-like body, whisk the cornstarch with 1 tablespoon cold water, then stir it in. For a thin pourable marinade, skip it.
Marinate. Pour over your protein in a zip-top bag or dish, turning to coat. Marinate 15–30 minutes for a quick meal, or up to a few hours for deeper flavor.
Cook. Grill, bake, or sauté — basting with fresh (unused) marinade as it cooks. Always discard marinade that touched raw meat.