Microwave the butter in a small microwave-safe bowl on high until melted. Whisk in the hot sauce and lemon juice and set aside.
In a large bowl, whisk together olive oil, water and salt. Add the cauliflower florets; toss until well coated. Spread the cauliflower on a rimmed baking sheet and roast until beginning to brown and just tender about 20 to 25 minutes.
Whisk the hot sauce mixture, drizzle over the cauliflower and toss with tongs to coat. Roast the cauliflower until the sauce is bubbling and browned around the edges, 5 to 7 minutes more. Serve hot with bleu cheese dressing and celery sticks.