I love how you think Berry. You think like a scholar of literature, looking carefully at the words and considering their associations. Absolutely, the word "long" is extremely important to the story and its meaning. Throughout there are long walks for both "protagonists" (great that you use this word), and it will be a long while before the walks are no longer necessary. And you are certainly on the right track about how Salva will "alleviate" the problem of water scarcity. Some of the words you use here are very advanced and they are used in exactly the right context, for instance "discrepancy."
But this is my favorite part: "because the most important element is water,so.. i think the point of connection is water." Again, written like a scholar of literature and very astute!