Within "_property_expression_names_comment" it says to "Leave it blank to get 'normal' terrain." however when I used "elevation": "" no water was generated at all on the map (including non in the starting area) after chaning it to "0_16-elevation" it then started placing water so I feel that they is either a bug with the config loader or that there has just been a mistake with the comment in the file.
Thank you for looking into this report, see below for full map gen settings.
map-gen-settings.json