A WaterMonitoringObservation is defined as a specialisation of the O&M OM_TimeSeriesObservation class as shown in Figure 4. This specialisation allows for more specific use of O&M to be defined according to the commonalities of in-situ hydrological observations. The following requirements are defined for this specialisation of OM_Observation: Req 1 A WaterMonitoringObservation shall have a result of type Timeseries, as defined in section 10 of this standard. Req 2 A WaterMonitoringObservation shall have a featureOfInterest of type SF_SpatialSamplingFeature, as defined by ISO19156, which includes WaterSamplingPoint defined in section 8.3 of this standard. Req 3 A WaterMonitoringObservation shall have a procedure property of type WaterObservationProcess, as defined in section 8.11 of this standard. Req 4 A WaterMonitoringObservation shall have a metadata property of type ObservationMetadata, as defined in section 8.2.8 of this standard. Req 5 A WaterMonitoringObservation shall have an observedProperty of type GFI_PropertyType, as described in ISO19156.