SCHEDULE I - Evoqua Water Technologies Corp. Condensed Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Condensed Financial Statements, Captions [Line Items]
General and administrative expense									$ (192,597)	$ (217,013)	$ (193,816)
Income before income taxes									121,766	1,116	9,266
Income tax expense	$ (4,035)	$ (740)	$ 7	$ (2,603)	$ (10,721)	$ (7,959)	$ 4,579	$ 4,514	(7,371)	(9,587)	(1,382)
Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 31,308	$ 21,384	$ 7,812	$ 53,145	$ 1,688	$ 4,135	$ 1,384	$ (16,730)	113,649	(9,523)	6,135
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Other operating income									16	73	78
General and administrative expense									(476)	(303)	(2,142)
Net income (loss) of subsidiaries									114,109	(9,293)	8,199
Income before income taxes									113,649	(9,523)	6,135
Income tax expense									0	$ 0	0
Net income (loss) attributable to Evoqua Water Technologies Corp.									$ 113,649		$ 6,135