Welshman protecting current source of bottled water (5)
I believe the answer is:
evian
'source of bottled water' is the definition.
(Evian is a trademark for bottled water)
'welshman protecting current' is the wordplay.
'welshman' becomes 'Evan' (common Welsh name).
'protecting' is an insertion indicator (inserted letters are held or protected).
'current' becomes 'I' (symbol for electric current).
'evan' enclosing 'i' is 'EVIAN'.
(Other definitions for evian that I've seen before include "spa town" , "springwater" , "This water" .)