DIY turbidity meters
BabyTurbiduino aka Daphna-2-MIDI Converter
See more info and file on Thingyverse
simple light absorbtion at a specific wavelength of a cheap laser, easy detection of turbidity.
turbidity to pd tools:
Commercial Turbidity Sensors
see this for dishwashers...
UV-vis absorbtion spectrophotometer
UV-vis spectrometer, would be even nicer, added white LED instead of laser, changing colors with simple light filters. but they have almost no UV, so added a UV led. turns out the CdS photoresistors are really slow and not very sensitive at UV also...
also we are working on a hacked line-scanner to look at the spectra after passing a prism or grating.