For this group, it's cold in the bath! (5)
I believe the answer is:
batch
'for this group' is the definition.
(a batch is a group or set)
'cold in the bath' is the wordplay.
'cold' becomes 'c' (eg on taps).
'in the' indicates putting letters inside.
'c' going within 'bath' is 'BATCH'.
'it's' acts as a link.
(Other definitions for batch that I've seen before include "Set of items; instalment" , "Group of similar people" , "All the bread baked at the same time" , "A number of things produced at the same time" , "All the bread produced at one baking" .)