Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenues [Abstract]
Sales to external customers	$ 1,444,441	$ 1,339,541	$ 1,247,424
Cost of Revenue [Abstract]
Cost of product sales and services	(1,018,479)	(934,808)	(847,673)
Gross profit	425,962	404,733	399,751
Operating Expenses [Abstract]
General and administrative expense	(217,013)	(193,816)	(169,617)
Sales and marketing expense	(138,936)	(136,009)	(142,441)
Research and development expense	(15,300)	(15,877)	(19,990)
Total operating expenses	(371,249)	(345,702)	(332,048)
Other operating income	5,613	8,406	2,361
Other operating expense	(654)	(591)	(860)
Income before interest expense and income taxes	59,672	66,846	69,204
Interest expense	(58,556)	(57,580)	(55,377)
Income before income taxes	1,116	9,266	13,827
Income tax expense	(9,587)	(1,382)	(7,417)
Net (loss) income	(8,471)	7,884	6,410
Net income attributable to non‑controlling interest	1,052	1,749	4,247
Net (loss) income attributable to Evoqua Water Technologies Corp.	$ (9,523)	$ 6,135	$ 2,163
Basic (loss) earnings per common share (in dollars per share)	$ (0.08)	$ 0.05	$ 0.02
Diluted (loss) earnings per common share (in dollars per share)	$ (0.08)	$ 0.05	$ 0.02
Product
Revenues [Abstract]
Sales to external customers	$ 851,161	$ 802,302	$ 718,098
Cost of Revenue [Abstract]
Cost of product sales and services	(615,171)	(582,606)	(459,641)
Service
Revenues [Abstract]
Sales to external customers	593,280	537,239	529,326
Cost of Revenue [Abstract]
Cost of product sales and services	$ (403,308)	$ (352,202)	$ (388,032)