Prepare the Vegetables:
Combine sliced cucumbers, tomato wedges, and thinly sliced onion in a large bowl.
Mix the Dressing:
In a separate cup or small bowl, whisk together vinegar, water, sugar, salt, and black pepper until sugar dissolves.
Combine and Marinate:
Pour the dressing over the vegetables and toss gently to coat evenly.
Cover and chill in the refrigerator for at least 1 hour to allow flavors to meld.
