Definition:
nephelometric turbidity unit, a unit used in measuring water quality An instrument called a nephelometer (from a Greek word meaning "cloudy") measures turbidity directly by comparing the amount of light transmitted straight through a water sample with the amount scattered at an angle of 90° to one side; the ratio determines the turbidity in NTU's NTU measurements can be confused by the base color of the water from stains that may not create damage in the rock