We've Got A New Toy! - Analog Turbidity Sensor (SEN0189) - Mar2016

The turbidity sensor is able to detect suspended particles in water by measuring the light transmittance and scattering rate which changes with the amount of total suspended solids in water. As the TTS increases, the liquid turbidity level increases.

This sensor have both analog and digital signal output modes. You can select the mode according to the MCU as threshold is adjustable in digital signal mode.