1 cup water 1/2 cup distilled white vinegar 1/4 cup vegetable oil 1/4 cup sugar 2 teaspoons salt 1tsp black pepper 3 cucumbers, peeled and sliced 1/4-inch thick 3 tomatoes, cut into wedges 1 onion, sliced and separated into rings

Whisk water, vinegar, oil, sugar, salt, and pepper together in a large bowl until smooth; add cucumbers, tomatoes, and onion and stir to coat.
Cover bowl with plastic wrap; refrigerate at least 2 hours.