Has its main supplier, that's clear (5)
I believe the answer is:
water
'clear' is the definition.
The definition and answer can be both related to change as well as being verbs in their base form.
Perhaps they are linked in a way I don't understand?
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for water that I've seen before include "Compound of hydrogen and oxygen" , "Commonplace drink" , "Basic liquid" , "One of the four classical elements" , "What makes the Somme" .)