From Google Maps satellite image it looks like the farmland on the DR side of the border is far more expansive than the farmland on the Haitian side — maybe three times as large — so it's understandable that there is more need for farmland water on the DR side. But when it comes to the Dajabon/Ouanaminthe town, it seems that there are way more homes on the Haitian side, which means a need for water for human consumption.
It looks like there is another fairly large river, Yaque Del Norte, that's not too far to the east on the DR side, with a lot of farmland around it also.
This area, especially in the DR, seems to be a pretty productive farming area, and I wonder why there hasn't been an effort to dam sections (or pump water from them into a storage area) of these rivers so that in rainy months the excess water that isn't used and just runs off into the sea can't be stored for dry months.
An uncle of mine was the head of a dam project in Peru where they had to redirect a large river through a mountain in order to build the dam. It was quite a project that I believe was funded by the World Bank (my uncle worked for the WB). I believe that a part of the project was to direct water to a dry, desert area. Anyway, my point is, isn't funding available for projects that would solve problems related to food production? If so, why are governments not coming together to figure out a real solution to this problem instead of squabbling like mindless fools over leftovers?
This area is obviously a type of breadbasket (an important agricultural production area) for the two countries. This being the case, the area's importance, and need to become more productive, will grow as time passes.
Governing bodies, and the citizens, need to be looking way beyond the micro issues of today.