Turbidity sensors:

Smart phone version https://docs.google.com/drawings/d/1Z8tmVe19cu3z0X4PzvXQA7228orwcwIWU8alSdFUt20/edit * This version would need some sort of a container to hold the water sample. A clear container with a backing to reflect the flash from the camera. * Maybe a pattern is printed on the backing to help the camera focus and determine the clarity of the water. * Take one photo with the empty container to calibrate the flash power, then another with the water. * Exposure will have to be fixed for both photos so that the light doesnt change.

Simple version https://docs.google.com/drawings/d/182cRy51lv6cNB0RsvtAA62wYaFOjK9BNsgbsKE57bt0/edit * This version will use a light meter and a LED. * Simple PVC construction. * Water is collected in one part of the tube with a LED at one end and the light sensor set at 90 degrees.