Normal union leader is introduced to us on a lake (5)
I believe the answer is:
usual
'normal' is the definition.
(I've seen this before)
'union leader is introduced to us on a lake' is the wordplay.
'leader' indicates taking the first letters.
'is introduced to' indicates putting letters inside.
'on' is a charade indicator (letters next to each other).
'lake' becomes 'L' (geographical abbreviation).
The first letter of 'union' is 'u'.
'us'+'a'='usa'
'u' put inside 'usa' is 'usua'.
'usua'+'l'='USUAL'
(Other definitions for usual that I've seen before include "Normal, habitual" , "Customary - customary drink" , "Unexceptional" , "Drink repeatedly taken" , "not rum?" .)