Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Numerator for basic and diluted loss per common share—Net (loss) income attributable to Evoqua Water Technologies	$ 12,503	$ 3,198	$ 8,790	$ (10,401)
Denominator:
Denominator for basic net (loss) income per common share—weighted average shares	113,770	104,632	113,770	104,632
Effect of dilutive securities:
Share‑based compensation	5,445	3,109	5,773	0
Denominator for diluted net loss per common share—adjusted weighted average shares	119,215	107,741	119,543	104,632
Basic (loss) earnings per common share (in dollars per share)	$ 0.11	$ 0.03	$ 0.08	$ (0.10)
Diluted (loss) earnings per common share (in dollars per share)	$ 0.10	$ 0.03	$ 0.07	$ (0.10)
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)				8,901