Based on recent studies, Water-Based Nuclear Power Plants (NPPs) include onshore and offshore floating NPPs, gravity-based structure NPPs, and underwater NPPs. These NPPs are increasingly considered for their benefits, such as the floating NPPs ability to distribute energy to remote areas, offshore sites, and construction activities. Regarding safety, external hazards must be considered during the design phase as stated in the Head of Nuclear Energy Regulatory Agency Regulation Number 3 Year 2011 and Specific Safety Requirements-2/1 (Rev 1). The external hazards of Water- Based NPPs should differ from those of land-based NPPs. Several studies have outlined the external hazards that water-based NPPs only address, such as onshore floating NPPs, and have yet to discuss the impact on water-based NPPs' safety. This study reviews the external hazards that must be considered and their effects on all types of Water-Based NPPs. The study is conducted by reviewing national regulations and international references to identify specific external hazards for Water-Based NPPs, followed by examining scientific works related to marine safety and Water-Based NPP design information to understand the impact of external hazards on the facilities. The review indicates that the external hazards that need to be considered for Water-Based NPPs include weather hazards, human- induced external hazards, earthquakes, and tsunamis. Keywords: NPP, Floating NPP, External Hazard, nuclear safety