I had completely forgotten the SAA 747s initially operated with water injection.
Yes the early S.A.A. B747's coming in and out of Heathrow were looked after by those of us on the BOAC, then B.A. Foreign Ops Team. We were often called to fix the Water injection System.
The P&W JT9D's needed a little help getting full power during hot or high Ops.
The Water Injection system had a Tank in the Dry Bay, forward of the Centre Fuel Tank. High-Capacity Electric Pumps were located in the L/H and R/H Inboard L/E Edge Area.
Tank was topped up to full with De-Min water. We had a Bowser at Heathrow specially for Demineralised Water. Probably left over from the B707's..
Water Injection was selected and armed from the F.E.'s Panel from memory and the system would run at full bore when initiated with the 3 phase Pumps activated by the Thrust Levers position, almost at T/O Power, until the Tanks were drained.
Water was introduced into the Compressor front end and would apparently increase the density of the air going through the Engine to give it a little power margin at hot or high Airfields.
The Crews we talked to said it helped a little but wasn't really that effective and was a tad unreliable.
I remember when we used to function the system after repairing it, the function would be noticeable with electrical power draw on the APU or GPU and you had to be careful with it.
Hope that helps...