Here is a fun idea.
Make a copy of the original setup file (in case there is a screw=up)
Change defaultterrain to 500 (if should already be 500)
Change defaultwaterheight to 800
In the editor make a new map using the random terrain command
Select a high spot in the terrain and put down a start marker ( If you don't you will drown)
Run a test. All of the low spots in the terrain should fill with water. Son-of-a-gun you've got free lakes
Note when you are done with the map make sure you change the setup variables back to their original settings or
your other maps you load will be covered in water!!!!

EDIT: Additional info/warning
The two variables that allow this to work are found in Build 2017.04.10 Beta

nice like it

That settings only in the current beta. Unless lee's pushed it to the public preview since I last checked.

@Belidos
I checked steam and it shows I am using the public preview.
The map screen shots I provided are using the public preview which has the commands.

EDIT: Additional info/warning
The two variables that allow this to work are found in Build 2017.04.10 Beta which I assume will remain in future builds.

Makes for some interesting terrain options now that we know the elevation settings for water and terrain and can control these elevations individually.

Ah yes public preview, that's like an open beta that we can all access if we want, so yeah not everybody will be using it, but no reason to delete the thread, its very useful info, maybe edit and add that its in preview version not live.

Same random terrain map with the waterheight of 800 (used in my previous map) changed to 820. More lakes and larger lakes.
if you try a revised setup file remember to change the setup file back to the original settings of 500 default waterheight and default terrainheight of 500
or you will flood other maps when they are loaded in the future. If you forget it is not a disaster the setting can be revised at any time.

Note: the latest build 2017.04.19 Beta still contains the same setup variables

This is good to know, thanks, looks pretty cool.

Love to see this controllable in lua, it would be great as an additional challenge for the player to escape from, for example, a sinking ship,.

@Tarkus1971 agreed, Control over the water level via lua is something I've wanted for ages, would make for some nice challenges and effects.

Maybe that is why Lee separated the water height and terrain height in the setup text file. Here's hoping.