Water/water meth injection? Never had that on any B747 I flew
...
Or have I missed something?
Yes, you have missed something, it's a big wide world out there.
Someone has very kindly posted a nice summary of the 747 water injection system:
B747-200 Water Injection Take Off.
This very complicated water injection system could be used with the following JT9D engines on the 747 :
JT9D-3A, Dry T/O rating 43.500 lbs. Wet rating 45.000 lbs.
JT9D-7 and -7H, Dry T/O rating 45.500 lbs. Wet rating 47.000 lbs.
JT9D-7A and 7AH, Dry T/O rating 46.150 lbs. Wet rating 47.670 lbs.
JT9D-7F, Dry T/O rating 46.750 lbs. Wet rating 48.650 lbs.
Perhaps "drink'n & post'n" isn't quite your thing.