The autopsy of Whitney Houston revealed she did have water in her lungs when she died, but the medical examiner needs to determine exactly how much before they can rule whether she died as a result of drowning ... law enforcement sources tell TMZ. 

As TMZ first reported, authorities believe Houston may have fallen asleep or lapsed into unconsciousness in the bathtub and drowned.

But according to our sources, authorities cannot yet determine whether Houston died before she was submerged in the water or after. We're told there is still a possibility Houston was dead before she went under the water. 

Toxicology results will be back in 4-6 weeks.