What Mars Would Need to Have Water

Mars might have had water many years ago, but now Mars habitat make it impossible to have water on the surface of mars.  If Mars was to have water it would need a thicker atmosphere so it wouldn't be as cold.  Mars would need warmer temperatures to melt the ice to make water.  If Mars had water it would also need thicker air so water wouldn't turn into vapor.  If Mars had these things it would probably have water.