First of all I consider Dr. Filonov to be my mentor and don't see any reason to disagree with him. Hence, I just called him to get the answer from the horse's mouth.
First of all he wanted to underline that metabolic water is not produced just through fat metabolism but everything else as well, including tissues,etc. Secondarily he said how much metabolic water is produced during the dry fast is based on an individual, but an average it is between .8 to 1 liter per 24 hours. The 400 ml you've mentioned is produced in non-fasting condition. You are welcome to email him to double check if you like. Although he is currently in Altay mountains and won't be back on-line till the 20th of this month.