WASH interventions are essential to support human health, prosperity, and dignity, as they provide the base for an adequate standard of living. In many low- and middle- income countries, especially in rural and low-income areas, decentralized wastewater treatment systems (DEWATS) can offer a solution to convey, treat, and dispose of or reuse wastewater closer to the source and through smaller conveyance networks. In Indonesia, and as such in the Brantas basin in East Java, focus area of this study, the government has recognized DEWATS as their best available option for improving sanitation in dense low-income urban settings. Although the percentage of households with access to proper sanitation in the province of East Java has been increasing steadily, service coverage and the quality of sanitation systems still need to be increased to reach the desired coverage by 2024. Similar to other fields of application, within WASH and concerning DEWATS, stakeholder engagement is key to develop and strengthen integrated and sustainable approaches. Nonetheless, it is challenging to formulate targeted interventions in the watershed since they depend on the willing support of various stakeholders who may have different priorities (even within their own institutions), having diverse (and sometimes conflicting) viewpoints. This may result in stakeholders strongly contesting the appropriateness of various solutions. An exploration of stakeholder priorities is therefore needed to facilitate the application of wastewater treatment technologies. Due to its participatory approach and the type of interpretation that the method allows, Q-methodology was selected to explore this situation. Q-methodology is a set of techniques which allow for the study of ‘subjectivity’, combining statistics with the depth provided by qualitative data. It is composed of the data collection technique (called Q-sorting) and a data analysis step via correlation and factor analysis. In this research, the perspectives and priorities of various stakeholders regarding decentralized wastewater treatment solutions are explored to assess the applicability and acceptability of DEWATS in the Brantas river basin. This aims to identify context-based criteria and challenges to the implementation of DEWATS in the Brantas watershed. Although findings from Q-methodology cannot be generalized for a general population, the findings from this study show strong indication that Surabaya government workers tend to prioritize similar criteria, that Malang community members think more similarly than their Surabaya counterparts, and that if a respondent prioritizes the elements describing the 4-F1 perspective (Basic current needs; Long-term sustainability; Socialization and collaboration; High awareness; Economically conscious) then they are likely to be some type of specialist. Additionally, four distinctive perspectives were identified: a focus on long-term sustainability of the system, although with less defined stakeholder responsibilities; a pragmatic, need-based approach; a preference for community-led approaches with user-friendly systems and greater subsidy availability; and a collaborative, but still community-run, approach with a high feeling of ownership. Further research is needed nonetheless to identify how the levels of agreement and disagreement among the different groups for the various statements presented could be integrated into the design and decision-making process for DEWATS in the region.

This study investigates the connection between macro-scale parameters (MSP) and micro-scale water quality parameters (MSWQP) in the Brantas River, employing a multivariate linear regression (MLR) modelling approach. The analysis reveals several critical insights into the complex dynamics of water quality in this river system.

Key findings indicate that high-quality input data, both in terms of quantity and measurement frequency, play a key role in the effectiveness of predictive models. Seasonality is a useful predictor and is recommended to be supplemented with rainfall data to better capture its influence on runoff and water quality. The study introduces the concept of basin accumulation and the implementation of buffer areas, demonstrating that these enhancements lead to improved model performance.

In conclusion, it can be said that relying just on macro-scale parameters is insufficient to generate an effective linear regression model. However, with the right optimizations and useful input data, it can be an insightful and valuable tool for water quality prediction.

In this study, the relationship between water quality and agriculture in the upstream region of the Brantas catchment has been investigated, with a focus on Electric Conductivity (EC), Dissolved Oxygen (DO), pH, nitrate, Biological Oxygen Demand (BOD), phosphate and ammonia concentrations. The EC concentrations ranged from 120 to 570 μS/cm, the DO concentrations from 3.15 to 8.57 mg/L, the nitrate concentrations from 0 to 20 ppm, the nitrite concentrations from 0 to 3 ppm, the BOD concentrations from 6.22 to 6.87 mg/L, the phosphate concentrations from 0.25 to 1 mg/L and the ammonia concentrations from 0 to 0.25 mg/L. Using detailed land use data, the correlation between land use classes and water quality parameters was analyzed. Nitrate concentrations of streams of which the catchment area consists of over 70% Ladang area ranged from 2.5 to 11 ppm, while catchment areas consisting of over 70% of Kebun area featured nitrate concentrations of up until 4 ppm. Regarding EC, this difference is 200 to 475 μS/cm versus 200 up until 375 μS/cm. Certain parameter concentrations, in particular BOD, raise potential concern. While this research provides some insights into water quality in the Brantas catchment, it also underlines the need for further investigations employing improved methodologies, increased sampling over a larger timescale and area, and comprehensive, multidisciplinary approaches. It is recommended that further studies in the area focus more on different parameters, in particular BOD.