Able to read that tea can be made by the litre! (8)
I believe the answer is:
literate
'able to read' is the definition.
(I've seen this in another clue)
'tea can be made by the litre' is the wordplay.
'can be' indicates anagramming the letters.
'made by' is a charade indicator (letters next to each other) (letters written or made by another set of letters).
'the litre' becomes 'liter' ('liter' can be a synonym of 'litre').
'tea' is an anagram of 'ate'.
'ate' put after 'liter' is 'LITERATE'.
'that' is the link.
(Other definitions for literate that I've seen before include "well expressed" , "Well versed in books" , "properly educated" , "Erudite" , "Learned" .)