The increasing global demand on freshwater is resulting in nations improving their terrestrial water monitoring and reporting systems to better understand the availability, and quality, of this valuable resource. A barrier to this is the inability for stakeholders to share information relating to water observations data: traditional hydrological information systems have relied on internal custom data formats to exchange data, leading to issues in data integration and exchange. Organisations are looking to information standards to assist in data exchange, integration and interpretation to lower costs in use, and re-use, of monitoring data. The WaterML2.0 Standards Working Group (SWG), working within the Open Geospatial Consortium (OGC) and in cooperation with the joint OGC-World Meteorological Organisation (WMO) Hydrology Domain Working Group (HDWG), has developed an open standard for the exchange of water observation data. The focus of the standard is time-series data, commonly used for hydrological applications such as flood forecasting, environmental reporting and hydrological infrastructure, where a lack of standards inhibits efficient re-use and automation. This paper describes the development methodology and principles of WaterML2.0, key parts of its information model, implementation scenarios, evaluation and future work. WaterML2.0 was adopted by the OGC as an official standard in September 2012.