Cheap and nasty marble is waterless (6)
I believe the answer is:
tawdry
'cheap and nasty' is the definition.
(I've seen this before)
'marble is waterless' is the wordplay.
'marble' becomes 'taw' (taw is a kind of marble).
'is waterless' becomes 'dry' (similar in meaning).
'taw'+'dry'='TAWDRY'
(Other definitions for tawdry that I've seen before include "Cheap and flashy" , "Showy but cheap and nasty" , "Showy and gaudy but without real value" , "Vulgar" , "Cheap; sleazy" .)