Open-source water quality testing: turbidity 1

Turbidity refers to the dirtiness or cloudiness of a water sample. Technicians at water treatment plants regularly measure water turbidity before and after treatment. It’s a legal requirement in many countries, and one indicator of whether treated water is safe for human consumption.

The unaided eye can distinguish cloudy water from clear water, but even visibly clear samples of water can have dangerous levels of turbidity. The standard tool for measuring turbidity (a turbidimeter) is a complex piece of equipment. Handheld units capable of analyzing a single sample vial cost several hundred dollars; automated units capable of intermittently analyzing samples from a column of flowing water can cost several thousand. An affordable, open-source solution for turbidity sampling would be a major step towards assuring the quality and sustainability of programs that seek to expand global access to treated drinking water. Partly completed open-source turbidimeter projects can be found online, apparently abandoned.

This post is to announce a new effort to design an open-source turbidimeter. The design goals are:

(1) Turbidimeter costs less than $100 (for a production model),
(2*) Reads samples with an accuracy of 0.05 NTU in the sample range 0-5 NTU, and 0.2 NTU in the range of 5-20 NTU,
(3*) Reads samples with an accuracy of 5% in the range 20-1000 NTU,
(4) Can be operated manually, or in automated mode for continuous sampling,
(5) Transmits data to an Android phone, via USB connection or Bluetooth,
(6) Is powered by 2-4 AAA batteries,
(7) Can collect samples, automatedly, every 15-minutes for one month without needing new batteries.

I hope to have a model ready for field testing this coming January at gravity-powered, non-electric AguaClara water treatment plants in Honduras. Technicians at these plants record water quality and quantity data every two hours on paper, and five of these plants are participating in a pilot SMS-to-web monitoring program. You can view the fruits of their labor at

An open-source turbidimeter fulfilling the design goals listed above will not quite meet the strict technical requirements of the EPA, but will nonetheless provide a huge improvement over the status-quo of rural and small-scale water treatment monitoring, at a realistic cost.

Thus far I’ve been working with Dr. Monroe Weber-Shirk and Alex Krolick of AguaClara, and hope to find more collaborators soon. I’ll be posting a progress update in the next few days.


*Turbidity is typically measured in Nephelometric Turbidity Units (NTU). International standards for drinking water are 0.0 to 0.3 NTU, but anything under 5 NTU looks basically clear to the human eye.


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One thought on “Open-source water quality testing: turbidity

  • Miguel

    Dear Chris,
    First of all congratulations for the open source design.
    I am interested in monitoring a couple of stream in Spain and I would appreciate so much if you have any technical description of your device. The main purpose of my project is to implement this device on my classes.