Expanding access to water quality monitoring with the open-source WaterScope testing platform

Access to safely managed drinking water is a critical global health issue, affecting approximately one in four people. This is especially problematic in low-income countries, where waterborne diseases cause significant preventable mortality. While progress has been made in increasing access to safe water, the rate of progress needs to significantly accelerate to meet the UN Sustainable Development Goal 6.1 target of universal access by 2030. Microbiological water monitoring is crucial for improving WASH interventions. Effective testing technologies must be affordable, reliable, easy to use, and locally available to empower communities to proactively address water contamination issues. Current microbial water testing typically focuses on *E. coli* as an indicator of fecal contamination. Established methods often involve cultivation, which can be time-consuming and require specialized skills and equipment. Novel methods like biosensors and DNA amplification exist, but are not always suitable for low-resource settings, where many institutions fail to meet their water testing targets. Human-centered design (HCD) is vital in addressing practical barriers in the WASH sector, including high logistics and labor costs, and poor data management. Open-source designs facilitate participatory development, repair, and reduce reliance on proprietary supplies. This study presents WaterScope, an open-source, digital, and portable testing kit designed to address the challenges of water testing in low-resource settings.

Existing water quality testing methods, primarily focused on *E. coli* detection, range from traditional methods such as multiple-tube fermentation and chromogenic agar to more advanced technologies like biosensors and DNA amplification. However, many lack suitability for low-resource contexts due to complexity, cost, or requirement for specialized training and infrastructure. A significant body of research emphasizes the importance of human-centered design (HCD) in the development of WASH interventions to overcome practical barriers and improve user adoption. The literature highlights the challenges of high logistics and labor costs, poor data integration and interpretation, and limited access to consumables and parts. Open-source initiatives are promoted as a way to enhance accessibility, reduce reliance on proprietary technologies, and facilitate collaborative improvement. This review informed the design and development of the WaterScope system, focusing on addressing the identified shortcomings of existing testing methods within the context of low-resource settings.

The WaterScope (WS) kit was developed using an iterative HCD approach informed by extensive consultations with stakeholders (program directors, scientists, field technicians) and workshops involving potential end-users in diverse locations. Feedback on usability, ease-of-use, and desired features directly influenced the design. The WS kit utilizes a membrane filtration (MF) method, incorporating a reusable cartridge with a single-use membrane 'slider' for streamlined processing. The integrated microscope enables automated colony counting via machine learning (ML), reducing user error and facilitating digital data sharing. The system was validated through three distinct studies: 1. **Controlled lab experiments:** A comparison of WS with three established methods (Chromogenic Coliform Agar (CCA), Colilert-18, and Membrane Lauryl Sulphate Broth (MLSB)) using a five-fold dilution series of *E. coli* showed strong linear relationships and non-significant differences between WS and the reference methods. 2. **Controlled environmental validation:** A year-long study on the River Cam (UK) demonstrated excellent agreement between WS, CCA, and Colilert methods across a range of *E. coli* concentrations. 3. **International field trials:** Trials in South Sudan, Kenya, and Ethiopia, using Compact Dry™ as a reference, demonstrated the system's real-world performance and identified the need for improvements to sterilisation protocols to minimize false positives. User feedback from workshops was instrumental in iterative design improvements. Statistical analysis included linear regression, mean-difference plots, and Spearman rank correlation to assess the equivalency and correlation between WS and reference methods. ROC curve analysis was used to assess the performance of the system in field trials. A cost analysis compared WaterScope with alternative methods, considering kit cost, test cost, and operational expenses. Finally, the system's versatility was demonstrated by adapting it for colorimetric assays and clinical applications.

The WaterScope system demonstrated strong equivalence to conventional methods in quantifying *E. coli* in water samples, across diverse settings from laboratory to field environments. Key findings include: * **Laboratory Validation:** Strong linear relationships (R² values of 0.92, 0.84, and 0.75 between WS and CCA, Colilert, and MLSB respectively) and no significant differences at 95% confidence were observed between WaterScope and the reference methods in the laboratory experiments. * **River Validation:** High correlation (R² values of 0.95 and 0.94 with CCA and Colilert respectively) and no significant differences were found between WaterScope and reference methods in the year-long River Cam study. Spearman rank correlations were also very high. * **Field Validation:** While initial field trials in Juba, South Sudan, showed a higher rate of false positives, iterative improvements to sterilisation protocols and user training resulted in substantially improved performance in subsequent trials in Kenya and Ethiopia, achieving a false positive rate of just 5% in Addis Ababa. ROC AUC calculations showed substantial improvements in overall system performance. * **Usability:** User satisfaction surveys indicated high levels of satisfaction among users with prior experience of similar water testing systems. Those without prior experience initially found the system less intuitive during self-guided training, however satisfaction increased significantly after hands-on training. * **Cost-effectiveness:** The cost analysis showed that WaterScope is significantly more cost-effective than WagTech portable kits and comparable in cost to CompactDry methods, especially when considering the potential for lower costs with local production. * **Versatility:** The system's modular design allows for adaptability to other parameters and applications including colorimetric assays and clinical diagnoses. The system was shown to reliably detect bacterial contamination within 8 hours in a significant portion of the field samples.

The WaterScope system successfully addresses the need for accessible and reliable water quality testing in low-resource settings. Its accuracy, comparable to established methods, is coupled with significant improvements in usability, portability, and cost-effectiveness. The open-source nature of the platform enables collaborative improvement and adaptation, promoting local manufacturing and reducing reliance on proprietary components. The iterative development process, informed by user feedback, is a testament to the power of HCD in addressing the practical challenges of water testing in the field. While the initial field trials highlighted the importance of rigorous sterilisation procedures and user training, the subsequent improvements demonstrate the system's capacity for adaptation and optimization. The versatility of the WaterScope platform opens up new possibilities for expanded testing capabilities and applications beyond water quality monitoring, including clinical diagnostics.

WaterScope presents a significant advancement in water quality testing, offering an accurate, user-friendly, and cost-effective solution for low-resource settings. Its open-source nature fosters innovation and adaptation. Future research should focus on further reducing costs through local manufacturing, developing additional assays for diverse water contaminants, and exploring integration with existing disease surveillance systems to maximize its public health impact.

While the WaterScope system shows strong potential, some limitations should be noted. Initial field trials revealed challenges related to sterilisation protocols, highlighting the need for thorough user training and robust quality control measures. The system's reliance on digital infrastructure for data transmission may be a limitation in areas with poor connectivity. Further research is needed to fully evaluate the long-term durability and maintenance requirements of the system in diverse field environments.