The ATR-42 landed at Congonhas Airport (CGH) runway 17R. During rollout the aircraft began to veer to one side. Control was not regained and the airplane ran off the runway onto rough ground. After leaving the runway the aircraft’s undercarriage dug into soft ground and then struck a link taxiway where the nose undercarriage collapsed. CONTRIBUTING FACTORS (translated from Portuguese report) Operational Aspect a. Weather conditions – Contributed A light rain caused the presence of water on the runway, enabling the occurrence of hydroplaning. b. Infrastructure – Contributed The accumulation of water on the surface of the runway, as a result of inadequate drainage, lack of “grooving”, enabled the hydroplaning. c. Education – Contributed The pilot applied full pressure on the right pedal, generating a force to the left that contributed to the departure off the runway. During hydroplaning, the pilot should not apply pedal to the opposite side to which the aircraft slides; this fact was not covered during the instruction of the pilot. d. Application of command – Contributed In the face of hydroplaning, the pilot applied the right pedal, aggravating the departure of the aircraft to the left.