Gripper
I wasn't aware it was a system that the Trident used, although having spent many years watching various departures I had begun to think that something like that could be a good idea.
The BAC 111 with Speys certainly did employ water injection on some models. There was a terrible crash when somebody decided to fill the water tanks with kerosene.
Out of interest I flew as an F/E for Qantas who used water on take off for their 747-200's when necessary. The sim was a nightmare when checking water failure on take off and/or engine failure. (as I remember one water tank fed the left two engines and another the right) In those instances the F/E called the shots and it was difficult.
I never did a water take off for real. After the sim details I'm very glad I was spared the reality.
Kind regards
Exeng