Most of the map i see now use the water_info.xml.
Some of them has more than 700.000 lines (=700.000 water sources !).
It seems that they create water source for 8 blocks (8 for X position and 8 for Y position)
Late answer, perhaps a bit necromancy but I come back to 7d2d in cycles so perhaps I can still be of use although I am nearly sure KingSlayerGM has found a solution already long ago. That said, regarding the 700.000 lines in water_info.xml that is a absolute metric ton of water sources, possibly a lot of ponds and lakes.
So, that said if you want to have your water level at e.g. 40 the only approach I know is to make a or several water sources at that level on the map. I've tried finding all documentation on how water works and unless new documentation has been added somewhere by someone its not very likely that's there anything that was not covered in the guide I wrote back then.
Anyway, if you have any questions that you want answered feel free to quote me again as ill be around for a while
