The reason why Zhao Hai had chosen to learn the water control technique instead of the sound Attack technique was because the sound Attack technique was not his strong suit. Although he had never learned the water control technique before, one should not forget that there were Water-type spells among all types of magic. Furthermore, Zhao Hai could control water, so he thought that he would be able to learn the water control technique faster.
The water manipulation technique was not the most difficult. It only had two hand seals, the water-sky hand seal and the Dragon rope seal. With the addition of the spiritual Qi circulation technique, Zhao Hai believed that he could master it in a month.