Low Cost Turbidimeter

AguaClara needs a reliable and simple method for candidate communities to monitor the turbidity of their water supply. Portable turbidimeters cost $400 or more and thus are too expensive to provide to a large number of candidate communities. The goals of providing candidate communities with turbidimeters is to determine the source water turbidity range and hence the type of water treatment that will be required. For example, if the source water turbidity never exceeds 10 NTU, then it may not be necessary to provide flocculation and sedimentation. The turbidimeter should be very inexpensive (less than $20). It should have an error of less than 50%. One possible approach is to use a Jackson style turbidimeter (a long tube that you fill with water until you can't see the candle below the end of the tube). Instead of a candle you could use a waterproof LED in the bottom of a PVC pipe.

See Caroline for an example of turbidity tube that uses a Secchi disk. This method will be highly dependent on ambient lighting.

See The Turbidity Tube:Simple and Accurate Measurement of Turbidity in the Field for some previous research in this area.

Waterproof LEDs are availabe at low cost.

There are two operating modes for the turbidity tubes. Either they can be slowly filled until the light (or secchi disk) disappears or the tube is filled and then the light source can be submerged until it disappears. This later technique is simpler and makes it possible to repeat the measurement easily.