SCHEDULE I - Evoqua Water Technologies Corp. Condensed Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Condensed Financial Statements, Captions [Line Items]
General and administrative expense	$ (206,455)	$ (192,597)	$ (217,013)
Income tax expense	(10,080)	(7,371)	(9,587)
Net income (loss) attributable to Evoqua Water Technologies Corp.	51,482	113,649	(9,523)
Parent Company
Condensed Financial Statements, Captions [Line Items]
Other operating income	(1,073)	16	73
General and administrative expense	(426)	(476)	(303)
Net income (loss) of subsidiaries	52,981	114,109	(9,293)
Income before income taxes	51,482	113,649	(9,523)
Income tax expense	0	$ 0	0
Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 51,482		$ (9,523)