Water turf by the start of August (4)
I believe the answer is:
soda
'water' is the definition.
(soda water is a kind of water)
'turf by the start of august' is the wordplay.
'turf' becomes 'sod' (both can mean a piece of grass).
'by' is a charade indicator (letters next to each other).
'the start of' indicates taking the first letters.
The initial letter of 'august' is 'a'.
'sod'+'a'='SODA'
(Other definitions for soda that I've seen before include "pressurised liquid" , "Fizzy drink - chemical compound" , "Variety of pop" , "In the US, a sweet fizzy drink" , "Type of bread, water or fountain" .)