The wastewater crisis in megacities of the Global South is increasingly recognised. However, sector‐driven approaches (of river pollution, sewerage, or city‐wide drainage) have had limited success in tackling this multifaceted problem. This article seeks to dynamise debates by positioning the current crisis in relation to contests of knowledge. Focusing on wastewater governance in Delhi, the article explores the question which different knowledges about wastewater exist in scientific communities, governments, and amongst citizens. What is frequently understood as ‘expert’ knowledge of the Central Pollution Control Board, is juxtaposed with the ‘lay’ experiences of citizens residing in one unauthorised colony in East Delhi. Exploring both, the article provides insights on the mechanisms through which community experiences are excluded from policy deliberations, leading to major wastewater‐related problems being overlooked. The article then calls for enhanced attention to knowledge integration, thus strengthening the participation of citizens in formulation and implementation of wastewater programmes.