The Sustainable Development Goals (SDGs) give much greater attention to environmental concerns than the Millennium Development Goals. SDG6, the water sector goal, is also more broadly framed, as it recognizes conservation needs in addition to drinking water and sanitation. However, normatively speaking, SDG6 is still framed in adequacy and sustainability terms, downplaying the goal of justice. This is a serious lacuna. Intragenerational justice is fundamental to many environmental problems, and especially to water, because water is a common-pool, multiple-use and unidirectionally flowing resource. Most debates in the water sector—upstream–downstream sharing, intersectoral allocations and specifically allocation to in-stream conservation, water pollution, and even groundwater depletion—are about the ‘biophysical (in)justice’ caused by these characteristics of the resource. The debates then focus on how the outcomes may be made more equitable (within sectors) or fair (across sectors). Large interventions, such as big dams, create multiple benefits and costs across multiple users and sectors, focusing attention on procedural justice. Social inequities may add another layer, as they often correlate with biophysical injustice. While SDG6 recognizes conservation and public health needs, it fails to recognize the fundamental tension between these needs and other uses of water, and therefore the issues of equity, fairness, and/or procedural justice in allocating between them. Policy makers may be more comfortable with framing environmental problems as sustainability problems. However, researchers have contributed to this narrowing by framing environmental problems along disciplinarily fragmented lines. The idea of biophysical justice offers an interdisciplinary bridge that may help broaden the discourse.