Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ 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 Information Disclosure [Abstract]
Revenue from product sales and services	$ 383,861	$ 347,827	$ 351,663	$ 346,105	$ 412,468	$ 360,343	$ 348,628	$ 323,002	$ 1,429,456	$ 1,444,441	$ 1,339,541
Gross profit	122,648	110,234	111,206	105,715	130,327	111,294	95,611	88,730	449,803	425,962	404,733
Interest expense	(9,362)	(10,485)	(13,252)	(13,583)	(14,797)	(14,842)	(14,474)	(14,443)	(46,682)	(58,556)	(57,580)
Income tax (expense) benefit	(4,035)	(740)	7	(2,603)	(10,721)	(7,959)	4,579	4,514	(7,371)	(9,587)	(1,382)
Net income	31,138	21,841	7,910	53,506	1,954	4,290	1,573	(16,288)	114,395	(8,471)	7,884
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
Basic income (loss) per common share	$ 0.26	$ 0.18	$ 0.07	$ 0.46	$ 0.01	$ 0.04	$ 0.01	$ (0.15)	$ 0.97	$ (0.08)	$ 0.05
Diluted income (loss) per common share	$ 0.26	$ 0.18	$ 0.06	$ 0.44	$ 0.01	$ 0.03	$ 0.01	$ (0.15)	$ 0.94	$ (0.08)	$ 0.05