The adjective potable is more common in French, where taps and other sources of water may be labelled eau potable, 'drinking water'. Its first vowel is pronounced like that in 'note' or 'goat, NOT that in 'pot' and 'got': this restores it to its etymological root in Classical Latin in the verb pōtāre, with the long '-o-', 'to drink', which also gives us the formal word potations, '[alcoholic] drinks [in copious quantities, to excess]. In British English, it is a term restricted to fairly formal and technical registers.
Potable' means 'fit to drink', 'pure', 'of suitable quality fro human consumption [in a developed country]'. It is used mostly by civil engineers, architects and planners to distinguish the supply of clean water from that of 'grey water', which may be fine for irrigation and many cleaning purposes but is not necessarily fit for human consumption.
- There are a couple of jocular uses:
Some people pronounce it with a first vowel that rhymes with 'pot' and 'got' IPA: /ˈpɒt ɜ bɜl/: this is nearly always jocular, or an error. Properly speaking, pronounced like this the word should be one used in snooker and other table ball games where the object is to pot the balls (i.e. to send them into a pocket) ("Black is lying in a very potable position". Never pronounce potable with a short '-a-' in formal academic circles: it will be taken as an error, a joke or a facetious attempt to say 'I am not being serious', like someone asked an opinion of a particular wine hiding his ignorance by saying 'It's very potable',