Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Revenues [Abstract]
Sales to external customers	$ 1,464,429	$ 1,429,456	$ 1,444,441
Cost of Revenue [Abstract]
Cost of product sales and services	(1,007,077)	(979,653)	(1,018,479)
Gross profit	457,352	449,803	425,962
Operating Expenses [Abstract]
General and administrative expense	(206,455)	(192,597)	(217,013)
Sales and marketing expense	(143,110)	(136,167)	(138,936)
Research and development expense	(13,445)	(13,198)	(15,300)
Total operating expenses	(363,010)	(341,962)	(371,249)
Other operating income	5,743	61,662	5,613
Other operating expense	(768)	(1,055)	(654)
Income before interest expense and income taxes	99,317	168,448	59,672
Interest expense	(37,575)	(46,682)	(58,556)
Income before income taxes	61,742	121,766	1,116
Income tax expense	(10,080)	(7,371)	(9,587)
Net income (loss)	51,662	114,395	(8,471)
Net income attributable to non‑controlling interest	180	746	1,052
Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 51,482	$ 113,649	$ (9,523)
Basic income (loss) per common share	$ 0.43	$ 0.97	$ (0.08)
Diluted income (loss) per common share	$ 0.42	$ 0.94	$ (0.08)
Product
Revenues [Abstract]
Sales to external customers	$ 861,026	$ 839,857	$ 851,161
Cost of Revenue [Abstract]
Cost of product sales and services	(607,693)	(588,264)	(615,171)
Service
Revenues [Abstract]
Sales to external customers	603,403	589,599	593,280
Cost of Revenue [Abstract]
Cost of product sales and services	$ (399,384)	$ (391,389)	$ (403,308)