A Raindrop Journey

My original origin is so hard to remember. Was it high above the tallest skyscraper, the steepest mountain top or the sharpest planes ascent? Then again did I begin in the underground lakes below? Nevertheless my journey is a revolving one from air, down to land or sea. And back again. My form can go from liquid, to mist and to frozen ice. My date of birth could be dated back thousands of years. I can travel millions of miles over the earth. I am singular in nature but prefer to join the other drops in life.