I agree that the rotors (one or both) are warped.  water will not cause this situation. the rotors are exposed to water continually when the vehicle is driven in the rain.  Usually the cause is that the last time a wheel was removed and remounted, the mechanic used an air  wrench to tighten the lugs.  this will result in the lug nuts to be tightened unevenly. as the rotors heat and cool while driving, the rotors will warp.  the rotors can be turned, but late model vehicles are manufactured with rotors with very little or no extra metal to be turned.