When a page is moved from one title to another it should be done using the move button that at the top of the page instead of copying the text from one title and pasting it into an article at the other title  Copypaste is not appropriate because the history of the article gets separated  Thats what happened in this case when chlorination was moved to water chlolination  Since edits were made to the article before and after the copypaste the history of edits to the text became located in the history of two separate titles  Because of techinical limitations of Wikipedias software the only way of fixing this for an administrator to delete one article move the other article to the same title delete it again and then restore all the edits