Irrigate (5)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
water
'irrigate' is the definition.
(I know that irrigate can be written as water)
This is all the clue.
(Other definitions for water that I've seen before include "Common liquid" , "Diamond quality" , "What can produce solution" , "Drink - type of 1 across" , "Classical element" .)