Not sure if you are looking for a paragraph or a whole essay, but here is something you can start with and elaborate on:
A Long Walk To Water is an appropriate title for Nya’s story because it highlights her daily, extended journey to water in a place where she is not safe. Two things such as water and safety that we take for granted, Nya has to travel long hours and even get hurt in the process for. It shows her journey as a child who has to work hard for necessity.
A Long Walk To Water is an appropriate title for Salva because it depicts his story as a refugee. As Salva goes through dangerous situations, we see him develop as a person and how these situations affected him. It was a long walk, but he eventually found himself to be helping children that would go through the same thing as him. It was a long walk to refreshing, calming water for both Nya and Salva.