As I said in my earlier post, this was thirty plus years ago - barrels may have changed since then. However, back then the fitting at the top of the barrel, where you connected the beer line and the gas, could be unscrewed if you had the correct tool. Then in would go the water - exactly the same way as the beer/lager would go in in the brewery.Never did a case involving a WMC only pubs, so your story isn't that relevant.
Exactly.
Not sure how often it happens these days but back in the 70s and 80s it was not unknown - especially in WMCs.