thanks @Impetuous Wombat :D

Happy to help :)
************NOTE***********
Close Timberborn before re-opening the file or the changes won't work

@Impetuous Wombat
Thank you. I have not tried editing files yet, but doesnt sound too complicated.
I will try it out when I need another map size waterproof

For me its a bit too late, but it can save other people from losing their sanity
So your comment is definitly a lifesaver

Awesome idea! As an alternative to setting the water values by hand:
1 - Browse local maps and locate your map as [MapName].timber (turn "Show File Extensions" to on in file explorer or equivalent)
2 - Rename file to [MapName].zip
3 - Extract all files from the zip file
4 - open world.json in any text editor
5 - replace text (ctrl-H in most Windows editors):
"WaterSource":{"SpecifiedStrength":1.0,"CurrentStrength":1.0
with:
"WaterSource":{"SpecifiedStrength":0,"CurrentStrength":0
6 - save the file
7 - select all 4 files that were extracted from the zip file and then compress to zip file (right click for this option in Windows)
8 - rename the Zip file to [MapName].timber and place it in the maps directory it was originally in, overwriting the original
9 - ????
10 - Profit!

Very useful, thank you!