Researchers studying large-scale questions in hydrology, oceanography, and meteorology can work with existing data through myriad platforms that provide access to remote datasets and render said information in various graphical outputs for interpretation and analysis. A survey of 30 publicly available hydrometeorological data platforms reviews the current state of the art in water-data discovery and visualization. Such platforms best meet the needs of a diverse user community by providing valuable data content, facilitating data exchange, and supporting visual analysis. To provide datasets of value to wider audiences, data providers can emphasize building datasets that are not only voluminous but also proportionally content rich in geographic, temporal, and measurement breadth, through integration of complementary datasets and coordinated data collection programs. In support of efficient data interchange, including software-driven integration of complementary content, data providers should increase adoption of web services to share data, along with machine-readable formats. In addition, this work surveys best practices in visualization and advocates for graphical user interface features that provide the flexibility required to integrate heterogeneous datasets by both novice and expert end users. Features that stand out as particularly useful include comprehensive content filters for customizable data queries, multiparameter plotting, statistical analysis tools, and predictive visualization. Effective combination of comprehensive—as well as voluminous—content, widely implemented standards for efficient data interchange, and appropriate visualization flexibility in the next generation of tools provided as software services will empower a wide user community, spanning laypersons, students, and researchers.