The emerging field of water ethics analyses and explores the moral implications of particular human–water relations and practices. This article focuses on ethical aspects of planning, management and governance of water quality, in what I refer to as water quality ethics. In particular, I draw attention to the potential for incorporating the ethical perspectives of philosophers Giles Deleuze and Félix Guattari into water quality planning, management and governance, opening for exchange between these normative fields of policy and practice with speculative philosophy. Deleuze and Guattari’s ethics emphasises the rejection of externally imposed binaries and categories onto a deeply heterogenous and dynamic world. Therefore, I identify three potentially problematic moments in how water quality is defined and responded to according to these criteria. I provide examples of how abstract and universalising principles can obscure the complexity of individual situations and thus hinder the visibility of alternative solutions. In so doing, I note the possibility for the empirically oriented arena of water justice scholarship to be complemented by a philosophical approach that emphasises the situated, fluid and lively materiality of water and water quality.