Restrict the supply of liquid in rota (6)
I believe the answer is:
ration
'restrict the supply of' is the definition.
(I've seen this before)
'liquid in rota' is the wordplay.
'liquid' indicates anagramming the letters.
'in'+'rota'='inrota'
'inrota' with letters rearranged gives 'RATION'.
(Other definitions for ration that I've seen before include "Limited allocation of food etc in wartime" , "Restrict the supply of" , "Limit quantity as of food during scarcity" , "Quota" , "Parcel out scarce food, say" .)