Whitney Houston's family was told by L.A. County Coroner officials ... the singer did not die from drowning, but rather from what appears to be a combination of Xanax and other prescription drugs mixed with alcohol ... this according to family sources.

We're told Coroner's officials informed the family there was not enough water in Whitney's lungs to lead to the conclusion that she drowned.

Our sources say the family was told Whitney may well have died before her head became submerged.

Sources tell us ... Whitney's aunt, Mary Jones, discovered Whitney's body in the bathtub. Mary had laid out Whitney's dress for the evening on the bed and the left for about a half hour. When Whitney didn't come out of the bathroom, Mary entered, pulled Whitney out of the tub and began administering CPR.