Bottle up the remainder of the water (8)
I believe the answer is:
restrain
'bottle up' is the definition.
(I've seen this before)
'the remainder of the water' is the wordplay.
'the remainder of' becomes 'rest' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the water' becomes 'rain' (rain is a kind of water).
'rest'+'rain'='RESTRAIN'
Can you help me to learn more?
(Other definitions for restrain that I've seen before include "Keep in check" , "Keep under control" , "Stop" , "use handcuffs?" , "Arrest - confine - subdue" .)