Do you need to waterproof cement board?
Cement board is not waterproof. Hardibacker is not waterproof. Tile and grout are not waterproof. Cement board will not fall apart when exposed to water.
WonderBoard® Lite is not a waterproof barrier. If the area behind the backerboard must be kept dry, use RedGard® Waterproofing and Crack Prevention Membrane or Custom® 9240 Waterproofing and Anti-Fracture Membrane Do not use drywall fiberglass tape for this product.
Beside this, Is it OK for cement board to get wet?