Spa got alternative power as temporary measure (7)
I believe the answer is:
Here is my best explanation:
'temporary measure' is the definition.
'spa got alternative power' is the subsidiary indication.
'alternative' indicates anagramming the letters.
'power' becomes 'p'.
'spagot' anagrammed gives 'stopga'.
'as' is the link.
(Other definitions for stopgap that I've seen before include "Temporary solution", "Temporary substitute", "Substitute", "Temporary measure", "A temporary substitute or solution", "Makeshift", "Temporary fix", "Improvisation", "Temporary expedient" and "A temporary or impromptu substitute".)