I don't get this "water is like acid" thing for phals. Water is a necessity for every living thing. Standard phals are hybrids of species that originate mostly in the Phillipines, where as one author put it "in the dry season they get as much rain (water) in one day as we get in a whole year in San Diego".
Overwatering can certainly be a problem with phals in pots, but it's a Goldilocks thing: kept too wet, get rot. Kept too dry, mineral salts build up in the pot which literally do poison the roots.
Martine, I would recommend you read some of the excellent culture notes available for phals:
Canadian Orchid Congress:
The Canadian Orchid Congress
Big Leaf Orchids, click "information" in the tabs at the top:
Big Leaf Orchids - online phalaenopsis store
Bedford Orchids, scroll down to V A and B:
Bedford Orchids
These are notes about growing and blooming phals written specifically for new hobbyists by people who have grown phals for years, and won many awards for breeding and culture of them. A few minutes of reading what the experts say will repay you many times over in healthy and blooming phals.