Compared to the the problem of nitrogen fixing in a future without haber-bosch fertilizer plants, water use barely registers.

It does. This landrace grows in areas receiving high rainfall, and with high ambient humidity -- and in my experience it only produces the mucus in those conditions, which sadly is likely to limit its potential, at least without very significant extra breeding work.

I wouldn't be surprised if the gel/mucus produced was water absorbent and most of the water used in the mucus actually came from external sources.