I'm not a teacher.
(2) a. All such grafts will die from lack of water.
b. Farmers are losing crops for lack of water.
It may have something to do with the collocations:
"to die from/of" - in (2)a. the phrase "lack of water" is a substitute of some "unhealthy" condition and used the way we describe the cause of human death: He died from/of hunger.
"to lose something for lack of something", as in (2)b., means that the farmers are loosing crops because of (as a result of) lack of water.