The most convenient source of the CSV file for uploading a batch of results is a spreadsheet (XLS) that has not been transformed by pivot table, meaning each parameter result has a separate line specifying the sampling site, date and time etc.
See the attachment for initial .xls and added Tab for resultant .csv.
Where to find the entity_id for the Samples. The imported values are posted to the Analyte webform via the Water Sample node.