Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Numerator for basic and diluted income (loss) per common share—Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 793	$ 1,503	$ 9,585	$ (8,898)
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	113,842	104,821	113,842	104,821
Effect of dilutive securities:
Share‑based compensation	5,205	3,164	6,094	0
Denominator for diluted net income (loss) per common share—adjusted weighted average shares	119,047	107,985	119,936	104,821
Basic (loss) earnings per common share (in dollars per share)	$ 0.01	$ 0.01	$ 0.08	$ (0.08)
Diluted (loss) earnings per common share (in dollars per share)	$ 0.01	$ 0.01	$ 0.08	$ (0.08)
Employee Stock Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)				8,824