You must immerse the cauliflower in hot water to clean it. If the cauliflower is infested with bugs, hot water will kill the bugs as well as remove the contamination if any.  Add about 1/2 tsp of turmeric powder per quart warm water and allow the cauliflower florets to soak in for 2-3 minutes. You should see bugs either floating or at the bottom when you remove the florets.