Meaning of jumping into water depends on situation as per dream interpretation. People usually dream of jumping into river, lake, pond or sea and it simply means they want freedom. They are fed up with the current life. River is continuously changing and you are expecting same thing from life.
Meaning of dreaming of jumping into water also means you fear that you will not be able to live up to the expectation of others. The dream is a warning and is asking you to listen to your heart and not to satisfy others by doing things you do not like.
Dreaming of you jumping into water and not coming up means soon you will have suicidal thoughts or you will spoil your life.
Water is associated with life. The dream is asking you to change your priorities and do what you really want to do. It is asking you to stop pleasing others.