Monarch and Dan-Air ended up with a fairly major logistical operation to make sure barrels of de-min water were properly marked and positioned at airports around the network where they were required for the performance enhancement. The marking of the barrels was much clearer after the Paninternational accident mentioned earlier, when the de-min water tanks were accidentally filled with JetA1 with dire consequences.
Hand-pumping the stuff into the aircraft was generally the F/O's job on turnround unless you could "induce" a rampie into doing it. Unless I'm much mistaken, the BA 1-11-510EDs didn't have the capability and it fell into disuse during the latter days of the type's service even on the 517FE and 518FG aircraft with Dan-Air and British World, and the ex-BCAL aircraft that ended up with European Air Charter via BA.
I do recall standing not too far behind a Tarom 1-11 operating for Adria Airways in about 1985 and getting a little bit wet as the water at the very beginning of the take-off roll was simply ejected downwards and backwards from the aircraft onto a pathway below the runway. The "extra noise" probably explains why I'm having increasingly frequent arguments nowadays with the other half about being a deaf old git...