Trim about 1/2 inch from the top of the onion and peel the outer skin.
Flip the onion, root-end up, and make slices starting about 1/2 inch from the root down to the cutting board to create petals.
Mix the flour, paprika, garlic powder, cumin, oregano, thyme, cayenne pepper, salt, and black pepper in a bowl.
In a separate bowl, whisk together the buttermilk, eggs, and water until well combined.
Dredge the onion in the flour mixture, ensuring all parts are well coated. Dip the onion into the wet mixture, then back into the flour mixture for a second coating.
Heat oil in a deep fryer or large pot to 375°F. Carefully lower the onion into the oil, cut-side down, and fry for 10-15 minutes until golden brown and crispy.