Machine's very good — was first to get running water (4,6)

'machine's' is the definition.
(pile driver is a kind of machine)

'very good was first to get running water' is the wordplay.
'very good' becomes 'pi' (old-fashioned term for 'pious').
'was first' becomes 'led' (to lead is to go first).
'to get' says to put letters next to each other.
'running water' becomes 'river' (a river runs).
'pi'+'led'+'river'='PILE-DRIVER'