Gather ingredients.
Whisk flour, milk, water, baking powder, and salt together in a bowl until smooth.
Heat vegetable or canola oil in a deep fryer to 365 degrees F (185 degrees C).
Pat fish fillets dry with paper towels to help ensure batter sticks; dip fish fillets into the batter to coat.
Carefully lower fillets, one at a time, into hot oil. Fry several fillets at a time without overcrowding the pan, turning once, until cooked through and golden brown, about 2 minutes per side.
Drain fried fish fillets on a wire rack over a paper-towel lined pan.
Serve hot and enjoy.
