Water in San Jose and throughout the Central valley is totally fine to drink. The paranoid or those with fragile digestive systems may choose to buy bottled water; I travel with a filtration water bottle, because there may be lead in the old C.R. plumbing, but mostly I drank tap water.
Depending upon the season, drinking water elsewhere in the country may pose problems to some travelers. Most of the water drawn near Dominical comes from springs and artesian wells and may be contaminated with agricultural runoff. I didn't worry about it much, and in fact I never got sick once in 24 days from drinking the tap water in San Jose, San Isidro del General/Perez Zeladon or Dominical. The water near Aranel had a very slight, bitter sulphuric taste to it but wasn't bad and didn't make me sick either.
I hate the idea of bottled water, simply because I hate paying for something that should be nearly free. Also, I don't like discarding numerous plastic bottles. Just a tree-hugger, I guess.
