What's wrong with tap water in Tenerife?

[Perikles]

Call me an old cynic but I can't help wondering if the company involved in making the tap water taste not so nice is also involved in producing/selling bottled water? 

Almost certainly  It reminds me vaguely of the Elizabethan Blackadder whose doctor prescribes a long course of leeches, a treatment recommended by the owner of the largest leech farm in Europe.