This thesis is about Global Water Governance (GWG) – an overarching normative framework by which water management practices across all scales may be guided. More specifically, it seeks to develop an understanding of how Corporate Water Stewardship (CWS), and its facilitation of the inclusion of companies’ perspectives to address water issues, affects GWG. Understood as a form of market environmentalism – a doctrine premised on mutual synergies between environmental conservation and economic growth – CWS provides a channel for companies to participate in, as well as spearhead, a quest for more sustainable water management within and beyond their own operations. Despite a proliferation of activities undertaken by companies, CWS has attracted limited scholarly attention, and an overarching analysis of the effects that mounting corporate involvement has had on the global water discourse has so far been absent from scholarly debates. This research draws on over 500 documents published by companies, NGOs, and other organisations, alongside 50 interviews with key practitioners. It specifically questions: (i) the empirical context through which CWS emerged; (ii) the manner in which companies from various sectors conceptualise water and its management; (iii) the way CWS endeavours are legitimised and; (iv) the mechanisms through which companies exert influence. Chapters 4 to 8 comprise an analysis of the main research findings. Chapter 4 investigates why companies are interested in water issues, how companies frame them, and how CWS could materialise. Chapters 5 and 6 address how companies from different sectors engage in CWS in the contexts of water resources management, and Water, Sanitation, and Hygiene (WASH). Chapter 7 turns attention to how companies draw on non-conventional sources of authority to legitimise their activities, and Chapter 8 analyses how CWS influences GWG. When taken holistically, the thesis attests to the key point that the inclusion of companies in solving water issues matters; their presence changes the status quo of water governance. More importantly, the thesis goes beyond such assertions by pointing towards how it matters. It finds that, as a result of corporate involvement, water is being reconceptualised from an environmental and social risk to society, to an economic risk for businesses. Moreover, although companies may not be doing this in an ill-intentioned way, the research suggests that when they participate in water interventions, they alter GWG by promoting the commercialisation of water management, the valuation of water risk, and the liberalisation of water governance. Thus, although the involvement of companies may contribute to improving the management and governance of water across all scales, their involvement has to be matched with proper ‘checks and balances’ to ensure that CWS serves the public good, rather than simply contributing to private profit.