The singer’s family were told by officials that she did not have enough water in her lungs to immediately conclude that drowning was the cause of death.
She had taken a combination of the sedative Xanax and other prescription drugs with alcohol, and could have died before her head went under the water.
Houston had drunk alcohol shortly before getting into the bath. Photographs of her room, obtained by TMZ, showed her final meal which included an opened Heineken can and an empty glass of champagne.
She had eaten a hamburger, then taken a turkey sandwich and jalapeno peppers on a tray with her into the bathroom, apparently intending to eat them in the bath.
A police source told celebrity website TMZ it was possible Houston suffered a heart attack caused by a reaction to medication, but it was too early to definitively decide what killed her.