In a skillet over medium heat, fry bacon turning it occasionally. It should be crisp in about 8-10 minutes. Line a plate with paper towels and drain the bacon. Crumble into small pieces and set aside.
In a medium bowl, add broccoli, onion, sunflower seeds, cranberries and water chestnuts. Toss to combine and set aside.
In a small bowl, add mayonnaise, vinegar and sugar. Whisk to combine. Season with salt and pepper to taste.
Add dressing to broccoli mixture and toss to coat. Sprinkle with bacon and toss again. Cover and chill in the refrigerator until ready to serve.