ffm, WHO does not recommend bf for only one year in the west, it recommends 2. the UK gov't advises atleastoneyear_ because bf rates are so piss poor over here.
i am not aware of any WHO literature that recommends water to exclusively bf babies in any region of the world including desert and semi desert regions. in fact, it stresses its importance for example in sub-Sahara Africa for HIV+ women as it is the form of feeding which is most likely to keep a baby HIV-. Again, it is good nutrition in the mother that is key. by that i don't mean a Western diet or even a varied diet.
BTW, nothing wrong with cornstarch or cassava semisolids - both staples which i have eaten in my time and will eat again if presented to me. if B vitamin deficiency (the cause of kwaishiokor) can easily be alleviated with green leafy veg in a diet made up primarily of cassava or cornstarch. I mean locally grown greens, nothing special. Where i am from, the most abundant form of greens are the cheapest and easiest to grow - in fact, they grow like weeds.
is the cassava grown locally? if it is, then the leaves are rich in B vitamins which is missing from a diet made up of cornstarch and cassava. to remove the poison in the leaves, it has to be chopped and boiled. that's all.
from what little you have told me, solving the nutritional problems in adults and children where you are from sounds like educating the adults about what they can grow locally, that would solve some of the dietary needs.