I think you are right that sanus more correctly describes a healthy state, whereas saluber/salubris seems to be preferred to describe those things which bestow health. Some examples:
ex saluberrimis Galliae et Hispaniae
after the very healthy [climate]* of Gaul and Spain
Caesar, Civil War, III.2
*climate is implied because the contrast is with the bad climate of Apulia and Brundisium which is making the troops ill
eaque remoto, salubri, amoeno loco
[a house and land of your own] and that in a remote, healthy, and
pleasant locality
Cicero, Letters to Friends, 333 (VII.20), Cicero to Trebatius, Velia, 20 July 44
ut scribis, salubres repente factae sunt
[the resort town of Baiae], as you write, has suddenly become a
healthy spot
Cicero, Letters to Friends, 263 (IX.12), Cicero to Dolabella, December 45
- The waters of said spa town:
“Non haec, ut fama est, unda salubris erat”
"Those waters [of Baiae] were not, as rumour has it, healthy"
Ovid, Ars Amatoria, 258
chelidoniam visui saluberrimam hirundines monstravere …
celandine was shown to be very healthy for the sight by swallows …
Pliny the Elder, Natural History, VIII.XLI
- And, finally, food and drink:
ceu non saluberrimum ad potus aquae liquorem natura dederit, quo
cetera omnia animantia utuntur
[speaking of water] as if nature had not given us the most healthy of
beverages to drink, which all other animals make use of
Pliny the Elder, Natural History, XIV.XXVIII
tostum salubrius habetur
[chickpea] is healthier roasted
Pliny the Elder, Natural History, XXII.LXXII