Preheat the grill to 300°F to 400°F
Remove the stem and wash your cauliflower.
Melt the butter and pour ⅔ of it into the bottom of the cauliflower while you have it upside down.
Put the cauliflower right side up on a piece of tin foil. Pour over the remaining butter. Season to taste with salt, pepper, cayenne, and garlic.
Pull up the corners of the tin foil so that it makes a dish. Pour the water into the bottom of the dish and then seal the cauliflower.
Place it over direct heat and grill roast for 25 to 35 minutes.
Carefully remove the cauliflower from the grill and open the packet. Watch out for steam.