Unlike water, it can't really run cold (5)

I believe the answer is:

blood

I'm a little stuck... Click here to teach me more about this clue!

'unlike water' is the definition.
'blood' can be an answer for 'water' (thesaurus). I am not certain of the 'unlike' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for blood that I've seen before include "It's said to be thicker than water" , "vital liquid" , "Kinship; temperament" , "Fluid in veins" , "Male siblings -- sworn friends" .)

I've seen this clue in the Evening Standard.

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