The simple tool bringing clarity to South African water systems

Photo credit: Groundtruth

In South Africa, a simple test using a 'clarity tube' that measures the clarity of water has empowered citizen scientists to warn authorities of water pollution issues affecting their health and livelihoods. A new study has shown that the data from this method are reliable and can augment slower and more expensive laboratory testing. The tool has already been used to alert local authorities to water pollution issues affecting rivers and communities, and could be used internationally to monitor the Sustainable Development Goal (SDG) targets on water.

Pollution from wastewater treatment services can have a dramatic effect on life in rivers and the communities that depend on clean freshwater. As much as 80-90% of wastewater in the global South is dumped into water systems with little to no treatment.

A useful way to get an estimate of water quality and track pollution sources is to look at the level of suspended matter in the water - total suspended solids or TSS. The TSS in water gives an idea of how much light can penetrate the water, what the visibility for aquatic organisms such as fish will be, the potential for the water to contain some kinds of harmful organisms, and how costly the water will be to treat. TSS can be measured precisely in a laboratory, but governments in the global South do not have the financial or infrastructural capacity to implement this costly process to act on TSS-related pollution issues.

Using a clarity tube provides a simple, easy, real-time alternative anyone can use at the water source they want to test. One simply fills the long acrylic tube with water and looks down its length. At the end, there is a black target that can be moved closer or further. To take a reading, one measures the distance at which the target is no longer visible.

The clarity tube distance measurement has been shown by several studies of rivers around the world to be closely correlated with laboratory measurements of TSS, as was corroborated over several years of monitoring in different Southern African river systems by the new study.

During 2018 to 2021, the study team collected samples from the outlets of two wastewater treatment works in KwaZulu-Natal Province, South Africa, and measured the TSS in the samples both in a laboratory and using clarity tubes. The study also analyzed data collected by citizen scientists using clarity tubes to measure TSS at the outlet of the wastewater treatment works three times a day, every day from 2012 to 2019.

The study also found that clarity tube testing is consistent no matter who performs it. Both professional and citizen scientists collected data, and there was no significant differences between measurements taken by different clarity tube operators, or different measurements taken by the same operator.

The goal for establishing water clarity tubes as a widespread citizen science technique is not to replace traditional testing. Rather, it is to greatly expand the scope and frequency of water monitoring to identify when more detailed testing should occur.

For example, a key finding of the study is that water quality varied a lot during the day, due to the variable nature of wastewater treatment. This would not be picked up by the normal testing protocols, but was easily identified by dedicated citizen scientists.

The study was funded by Groundtruth, the International Water Management Institute (IWMI) through the CGIAR Digital Innovation Initiative, and the Duzi‐uMngeni Conservation Trust (DUCT), with incredible long-term contributions from volunteers.

Clarity tube testing may already be having an impact. During the course of the study, clarity tube measurements indicated that local wastewater treatment works were releasing untreated wastewater, reaching zero percent compliance with effluent composition regulations by mid 2016. This led to meetings between stakeholders, the works operators and municipal authorities based on the warnings provided by the citizen science clarity tube data. In a year-and-a-half following the meeting, compliance rose to 60-70% of the time.

For this reason, the study team are excited about the potential of clarity tube testing as a new means to monitor water quality and empower communities around the world, for example as part of monitoring to report on the SDGs. In the Limpopo River Basin, citizen science will be a key input into the Digital Twin being developed for water management authorities: a virtual representation of key processes in the water system that will allow decision-makers to simulate the impact of interventions across the water system.

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