Steering this back on topic, after the diversion which I am sure the mods will take care of.
In Great Britain, by law, tap water must be provided for free to workers/customers for both working places and licensed premises. Does a BA plane fall under the licensed premises so that they do not have a choice but to provide this ?
BTW, this is not a EU thing as in Germany there are no obligation to provide free tap water (water must be provided by licenses premises but it can be charged).