Shape of washer attached to source of water, tight (7)
I believe the answer is:
sparing
'tight' is the definition.
(thesaurus)
'shape of washer attached to source of water' is the wordplay.
'shape of washer' becomes 'ring' (I can't justify this - if you can you should believe this answer much more).
'attached to' means one lot of letters go next to another.
'source of water' becomes 'spa' (I've seen this before).
'ring' after 'spa' is 'SPARING'.
Can you help me to learn more?
(Other definitions for sparing that I've seen before include "Economic (with resources)" , "Moderate, economical" , "Scanty - merciful" , "Economical; having mercy" , "Thrifty" .)