This Note seeks to explore the interaction of two possibly competing systems: the international investment arbitration mechanism and the new face of environmental regulation based on new governance theories. The changes in ICSID toward greater transparency and engagement of the public have perhaps helped states defend expropriation challenges when the state is seeking to protect the health and safety of its citizens’ drinking water. This Note will explore two ICSID arbitrations involving water regulation and the submission of amicus briefs: Methanex Corp. v. United States22 and Biwater Gauff (Tanzania) v. The United Republic of Tanzania. Both cases involve a foreign investor challenging a state’s action as an expropriation, or taking, of their investment. This Note explores the difference between the two cases in light of new governance theories of regulation and the procedural improvements in ICSID arbitration.