With less than a decade left to deliver the Sustainable Development Goal of universal access to water and sanitation, innovative and inclusive new approaches are needed to address the ongoing challenge of urban Water Supply and Sanitation (WSS). WSS has long been misrecognised as a technical issue of facilities and infrastructure, obscuring the complex socio-political drivers that shape distributional injustices in service provision. Furthermore, marginalised groups disproportionately suffering WSS injustices, such as informal settlement residents, are typically excluded from the WSS decision-making that could alleviate their struggles. The co-production of knowledge through partnerships with informal settlement residents is gaining interest as a potentially transformative method to address WSS injustices through improving recognition of the multifaceted and heterogeneous realities within informal settlements and empowering the political participation of informal settlement residents. Despite widespread academic enthusiasm, much of the literature remains broadly conceptual. This dissertation contributes to the debate by examining how knowledge co-production can help alleviate WSS service provision injustices through the specific case of the Centre for Community Initiative’s activities in the informal settlements of Dar es Salaam, Tanzania. The combined theoretical lenses of environmental justice and Feminist Political Ecology deliver a nuanced perspective on knowledge co-production that emphasises the importance of local context, heterogeneity within and between informal settlements and the complexity of ‘transformative change’.