Hobbes, thanks, but it did not help, unfortunately.
Having found out experimentally that to achieve its goal, in terms of virtualization of water, it is almost impossible, I came to the conclusion that it can be done through only the code.
Comrades programmers, you are doing fantastic things with the game for a very long time. An example of this is OpenXComExtended and OpenXComExtended +, which introduce a lot of useful, and extremely complex functions in the game. And I have an offer for you.
Now it is impossible to make missions on the water in the UFO and build bases on it. This means that somewhere there are properties of water where these things are prescribed. This, in turn, means that they can be changed. I do not think that carrying the code for water from TFTD is the not right way. It will be more correct to add the one that is in the UFO. In the presence of prohibiting encodings in water features, they can be simply removed.
1) Assign a unique "textures: id:" to the water, but not under the number, but with a unique name. On this "id:" allow to assign "terrain:".
2) Allow on the water to build bases.
3) Allow the UFO points to remain when they fall and land.
4) Allow missions.
I'm not a programmer, and programming languages not know, and i could not do. But you can. You've already done a lot of much more complicated things.
If I'm wrong - just say that I'm a fool and I'll leave you alone and bury my stupid ideas.