Have you tried to explain why and shown him exactly how much water he wastes?
(Break it down into cans eg 15 Coke cans.I saw this on a notice in a camp in the US I first worked in about 16 years ago and it has stayed with me forever.)
I can understand that people do it if they're not used to the idea of water as a resource which has to be used properly, but why, once they've had it explained to them, do people insist on running water away unnecessarily? I'm really puzzled by this. Is he just doing it to wind you up?
Moondog is right to be angry, though not at British water users. The anger should be directed at British people because they support EU trade restrictions that make these countries so poor that they can't feed themselves properly or build decent infrastructure.
Thousands of well fed white British people are quite happy to march through the streets about the "rights" of British farmers to buy new Range ROvers, but coloured people trying to feed their familieis are seen as "unfair competition" and their produce kept out.
This has recently taken an even nastier term where the farming lobby has managed to get dopey green media types to complain about the "wasteful" shipping of food over large distances.
Note we see this a lot. Do we ever see the same rage about growing crops in Britain that are require large inputs of energy ?
Wonder why ?