The turbidity sensor detects water quality by measuring level of turbidity.
It 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 (TSS) in water.
As the TTS increases, the liquid turbidity level increases. 

This turbidity sensor has both analog and digital signal output modes. You can select the mode according to the MCU (ie Arduino or Fishino) as the threshold is adjustable in digital signal mode.

Turbidity sensors can be used in the measurement of water quality in rivers and streams, wastewater and effluent measurements, sediment transport research and laboratory measurements.

Technical specifications

Operating Voltage: 5V DC Operating Current: 40mA (MAX) Response Time: <500ms Insulation Resistance: 100M (Min) Output Method:Analog Analog output: 0-4.5V Digital Output: High/Low level signal (you can adjust the threshold value by adjusting the potentiometer) Operating Temperature: 5℃~90 ℃ Storage Temperature: -10℃~90℃ Weight: 30g Adapter Dimensions: 38mm*28mm*10mm/1.5inches *1.1inches*0.4inches

Documentation

Wiki page