Rich supply of water awaiting attention (4-2-2)
I believe the answer is:
well-to-do
'rich' is the definition.
('well-to-do' can be similar in meaning to 'rich')
'water awaiting attention' is the wordplay.
'water' becomes 'well' (well water is a kind of water).
'awaiting attention' becomes 'todo' (I can't justify this - if you can you should give a lot more credence to this answer).
'well'+'todo'='WELL-TO-DO'
'supply of' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for well-to-do that I've seen before include "Fairly rich, prosperous" , "Rich; old towel (anag.)" , "'Prosperous, wealthy (4-2-2)'" , "Affluent" , "Fairly wealthy" .)