Rubber and plastics are unexpectedly weak against water, so that lifetime of molded products used in the presence of water is shorter than that in the absence of water, and some troubles are taken place by water. This is because that rubber and plastics, especially degraded polymers adsorb water. As a result, residual chlorine in tap water penetrate into the molded products to accelerate degradation. Furthermore, antioxidants in the molded products elute by micro- and macro- Brownian motions of molecular chains. It is recommended to select phenol type antioxidant and ethylene unit rich type EPDM for compound design of rubber with water resistance.