A natural runner, that's clear (5)
I believe the answer is:
water
This clue could be a double definition.
'a natural runner' is the first definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'clear' is the second definition.
The answer and definition 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?
'that's' is the link.
Can you help me to learn more?
(Other definitions for water that I've seen before include "non-alcoholic drink" , "H20" , "Basic liquid" , "Inundate" , "What can produce solution" .)