I know this is a weird question, and not typically the thing they would teach you guys - but I was talking with a friend today and we were kind of arguing - how much water would someone have to inhale to drown?
Rosen's says the following: (I had never heard anyone say that dry drowning was bogus until I just read this passage)
The classic hypothesis was that 10% to 15% of drowning victims die without aspirating a significant amount of water. Death from such "dry" drowning putatively results from severe laryngospasm causing hypoxia, convulsion, and death without fluid entering the lungs. An exhaustive review of the literature fails to corroborate this hypothesis  Dry drownings more appropriately reflect deaths from causes other than simple submersion."
Tough question to answer... no, impossible. How could you find out? Measure how much water is in a corpses lungs? How do you know that air didn't escape after death and get replaced by air? How could you know how much water in the lung was leakage from dead pulmonary tissue? If there is no water in the lungs, how do you know that the patient didn't have cardiac arrest, and just happened to be in the water? You can't test for arrythmia at autopsy.
Lets design a study. We need big numbers to get at the minimum amount, so lets take 1,000 healthy volunteers and put them in an enclosed tank and watch them die. We will have a measuring device at the top that can measure released air (which will only be from the patient, since the tank will be completely full of water). At the moment that the patient expires, we will measure how much air was released into the tank, and therefore, know how much water got into the patients' lungs prior to expiration.
I think that would be the best way to find out.
25. Modell JH, Bellefleur M, Davis JH: Drowning without aspiration: Is this an appropriate diagnosis?. J Forensic Sci 1999; 44:1119.