Well
If you can't do it any other way, what regions truly are, are values bewtween the top left corner (x1, y1) and the southern corner (x2,y2) and when you check if a position/coorinate is in a region/rect, you are checking
If x coordinate is > x1 and < x2 And y coordinate > y1 and < y2
Once you understand that concept, you can make regions of any size, shape, anything!!!
It might take long as hell, but you can specify all the parts that are water using some massive function check in JASS
I don't know enough about JASS to write out the function, but I can conceptualize it, something that would be a boolexpr
Would somebody be kind enough to build + show a boolexpr similar to the one discribed above that would cover water terrain in a small map? (show a picture of the map with an arial view)