This is a data interchange content model for an observation of the chemical composition of an aqueous fluid. A header content model for sample characterization, location, and analysis metadata is included to assist users finding analyses for specific samples, locations, time intervals, etc. Typically water temperature at the time of sampling are recorded along with sample data. Several 'suites' of analytes representing common analysis results are defined, with the intention that an implementation of the content model would offer several observation feature types, each of which consists of the header fields combined with the analytes for a suite. A content type for reporting results for a single analyte is also proposed, with an abbreviated header; this could be implemented for services similar to the EPA storet data services. In this approach a single analysis result is delivered as a collection of observation records, each with the same AnalysisURI and reporting single analyte. AqueousChemicalAnalysis-BasicData contains fields for information used to discover and retrieve chemical analyses meeting various criteria, and to evaulate the reported results. These fields would be reported along with a collection of analytes from the different suites proposed on the suites table.