Robert Cahill Henderson, an Ekaterina agent, had come extremely close to getting all 39 clues. However, the explosion of Krakatoa destroyed all his work. After he lost everything he realized that the last Ekaterina clue he needed was water, which was surrounding him the whole time. He wrote a poem that included the lines, "The very waves sang the song I knew." and, "Like Newton's discovery it fell on me" to ensure that none of his ancestors would make the same mistake he had.
Water is a liquid that is vital for life. Human beings will die without water within three days or 72 hours. Water is also commonly known as H2O, meaning that it is formed by two hydrogen atoms and one oxygen atoms. Earth is 7/10ths water and the human body is 75% water.