Waste water keeping streetcar in LA blue (11)
I believe the answer is:
ultramarine
'blue' is the definition.
(I know that ultramarine is a type of blue)
'waste water keeping streetcar in la' is the wordplay.
'waste water' becomes 'urine' (synonyms. I am not sure about the 'waste' bit.).
'keeping' indicates putting letters inside (some letters kept inside).
'streetcar' becomes 'tram' (synonyms).
'in' indicates putting letters inside.
'tram' put within 'la' is 'ltrama'.
'urine' enclosing 'ltrama' is 'ULTRAMARINE'.
Can you help me to learn more?
(Other definitions for ultramarine that I've seen before include "Vivid blue" , "Blue pigment originally made from lapis lazuli" , "See a colour" , "Deep blue pigment" , "one of the colours" .)