Groundwater is one of the most important natural resources in the world, comprising 97% of the accessible freshwater resources . The global utilization has expanded over the past 60 years due to increased availability of cheaper drilling and pumping technologies , increased pollution of surface water and population growth concurrently, many nations look toward groundwater as an alternative source of fresh water to accommodate their needs. In addition, groundwater, like surface water, is a fugitive resource which does not conform to administrative or political boundaries , hence many aquifers are transboundary. Considering the aforementioned, groundwater in international water resources law has its limitations. Firstly, the scientific and technical knowledge of groundwater and the complexity of hydrogeology contribute to the difficulty of assessing transboundary groundwater availability and boundaries . Secondly, in many states where groundwater is linked to land ownership, territorial sovereignty is a concern and are hesitant to share its management . In those cases where it is not linked to land ownership, the hidden nature of the resource also precluded policy makers to treat the resource as a mined resource similar to oil or gas. Thirdly, the limited and insufficient inclusion of groundwater and its special needs in international water agreements as compared to surface water is also an issue . In spite of these reasons, recent developments by inter-governmental and non-governmental organizations have increased efforts to promote the development of an international legal regime for groundwater. The International Law Association first included groundwater in its 1966 Helsinki Rules , but its limited scope led to the 1986 Seoul Rules . In 2004 the ILA further contributed as it developed the Berlin Rules, which has a chapter dedicated to transboundary groundwater . The United Nations International Law Commission's (UNILC) 1997 Convention on the Non-Navigational Uses of Water (hereinafter the 1997 Convention) was a significant point for the international regime on groundwater as it formally stated the application of customary international law for the international management of groundwater , however it only covers one classification of aquifers and has not yet entered into force . Five years later the UNILC embarked on Draft Articles on the Law of Transboundary Aquifers which is built upon the work of the ILA and its Helsinki, Seoul and Berlin rules and aims to codify the progressive development of groundwater in international law but it is also not without its faults . Besides the work of the ILA and UNILC, there have been other contributors. The Bellagio Draft Treaty is another important document recognized as an important advancement on transboundary groundwater management however is application in practice has been minimal . In addition, the Internationally Shared (Transboundary) Aquifer Resource Management Program (ISARM) was developed by UNESCO's International Hydrological Program during its sixth phase to promote the integrated and sustainable management international river basins and groundwater resource systems . The ISARM Project identified six transboundary aquifers of regional importance one of which is the Guarani Aquifer System in South America. The Guarani Aquifer System, named after the indigenous tribe living within the area of the aquifer, covers a geographic area of 1,087,879 km2 with an estimated volume of 30 trillion m3 under the nations of Argentina, Brazil, Paraguay and Uruguay . In 2000, Argentina, Brazil, Paraguay, and Uruguay initiated the Environmental Protection and Sustainable Development of the Guarani Aquifer System Project (PSAG) , with the support of GEF, OAS and WB to study and plan for the long-term management of the SAG . The aim of the PSAG was to develop and implement the first comprehensive transboundary management framework on groundwater . The PSAG concluded in January of 2009, falling short of its objective "to have a technical, legal, and institutional framework for the management of the protected Guarani Aquifer System." However, the project did develop a plan for the Coordinated Management Framework of the SAG in accordance with the Strategic Action Plan (SAP) of the PSAG, with the long term vision of the four nations to develop and implement the PSAG's original objective. The work done by international intergovernmental and non-governmental organizations as well as other experts has contributed to the progressive development of groundwater in international water law. However, the limitations of groundwater in international water law, the inconsistent state practice and limited international treaty practice conclude there is no consensus on an international legal regime for transboundary groundwater. The Coordinated Management Framework applied the principles and obligations of international customary law for the management of the SAG. In so doing, the questions of what are the principles and obligations necessary for an international legal regime on groundwater; what are the limitations of groundwater in international water law; how did the PSAG address the limitations to develop the Coordinated Management Framework; and how were the principles and obligations necessary for groundwater in the development of the Coordinated Management Framework will be investigated. The Coordinated Management Framework was analyzed with respect to the five elements an international agreement. 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