The development of markets in water quality, biodiversity and carbon sequestration signals a new intensification and financialisation in the encounter between nature and late capitalism. Following Neil Smith's observations on this transformation, I argue that the commodification of such 'ecosystem services' is not merely an expansion of capital toward the acquisition or industrialisation of new resources, but the making of a new social world comparable to the transformation by which individual human labours became social labour under capitalism. Technologies of measurement developed by ecosystem scientists describe nature as exchange values, as something always already encountered in the commodity form. Examining these developments through specific cases in US water policy, I propose that examining this transformation can provide political ecology and the study of 'neoliberal natures' with a thematic unity that has been absent. I understand capital's encounter with nature as a process of creating socially-necessary abstractions that are adequate to bear value in capitalist circulation. Such an argument supersedes the issue of nature's materiality and points toward a common language for the analysis of both humans and nature as two participants in the labour process. Political ecologists struggling with the commodification of nature have tended to overlook the social constitution of nature's value in favour of explicit or implicit physical theories of value, often as more-or-less latent realisms. I suggest that critical approaches to nature must retain and elaborate a critical value theory, to understand both the imperatives and the silences in the current campaign to define the world as an immense collection of service commodities.