This paper describes the concepts and procedures for the design and implementation of a water turbidity sensor.  It is designed with the purpose of offering us water turbidity readings.  The sensor is designed according to the standard ISO 7027 "The water quality, determination of turbidity", which specifies four methods for the determination of the turbidity of the water.  The light source is an infrared led to 850 nm which is modulated in frequency to prevent external light interference, so that the sensor receiver is immune to external sources of light.  The calibration of this sensor gets a sensitivity of 0.0014 V/NTU and a non-linear error less than 10%, for a range between 0.1 NTU to 600 NTU.Keywords: Turbidity, Nephelometer, Turbidimeter, Sensor, Calibration Curve