Source of water before summer (6)
I believe the answer is:
spring
I believe this clue is a double definition.
'source of water' is the first definition.
(I've seen this before)
'before summer' is the second definition.
(Other definitions for spring that I've seen before include "Leap - opposite to 15" , "Leap - part of year" , "The bouncy season" , "split" , "Does the house out thoroughly" .)