I have been told and read that a lot of drowning dreams are due to anxiety and stress. It's the idea that you are being overwhelmed. Now, with someone else drowning in your dream, it could be that you are either stressed and it relates to them or my better guess would be that you feel helpless about some stressor in your or their lives. I have a psych background, but not in dream psych, so these are just educated guesses.
I go this off a site:
To dream that you are drowning, signifies that you are overwhelmed by emotions or repressed issues that is coming back to haunt you. You may be proceeding too quickly in trying to discover your unconscious thoughts and therefore must proceed more cautiously and slowly. If you drown to death, then is refers to an emotional rebirth. If your survive the drowning, then a waking relationship or situation will ultimately survive the turmoil.
To see someone drowning in your dream, suggests that you are becoming too deeply involved in something that is beyond your control. Alternatively, it represents a sense of loss in your own identity. You are unable to differentiate who you are anymore.
To dream that you rescue someone from drowning, indicates that you have successfully acknowledged certain emotions and characteristics that is symbolized by the drowning victim.
**See The Meaning In Action: "Dogs In The Bathroom"