In a large bowl, whisk together flour, water, garlic powder, onion powder, and salt until smooth to create a batter.
Add cauliflower florets to the batter and toss until evenly coated.
Preheat air fryer to 375°F for 3 minutes.
Spray the air fryer basket generously with cooking spray. Place battered cauliflower in a single layer (work in batches if needed).
Air fry at 375°F for 12 minutes, shaking the basket halfway through, until golden and crispy.
While cauliflower cooks, mix buffalo sauce and melted butter in a large bowl.
Transfer cooked cauliflower to the buffalo sauce mixture and toss gently until well coated.
Return sauced cauliflower to the air fryer and cook for an additional 3 minutes to set the sauce.
Serve immediately with ranch or blue cheese dressing and celery sticks on the side.