Abstract: Substrate treating apparatus and methods are provided. The substrate treating method may include supplying a first side of a substrate with a first chemical solution from a first supply unit, supplying a second side of the substrate with a second chemical solution from a second supply unit, collecting a third chemical solution into a collect vessel, supplying the second supply unit with the third chemical solution to store a fourth chemical solution in the second supply unit, supplying the first side of the substrate with the first chemical solution stored in the first supply unit, and supplying the second side of the substrate with the fourth chemical solution stored in the second supply unit. The third chemical solution may be a mixture of the first and second chemical solutions. The fourth chemical solution may be a mixture of the second and third chemical solutions.