Area of water, pure (4)

I believe the answer is:

mere

I believe this clue is a double definition.

'area of water' is the first definition.
(I've seen this before)

'pure' is the second definition.
(I've seen this before)

(Other definitions for mere that I've seen before include "President Hollande's mother?" , "Pure; lake" , "sea" , "Previously pure" , "Lake; Wiltshire town" .)

I've seen this clue in The Times.

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