Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Numerator for basic and diluted loss per common share—Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 1,384	$ 12,503	$ (15,346)	$ 8,790
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	114,525	113,770	114,525	113,770
Effect of dilutive securities:
Share‑based compensation	4,188	5,445	0	5,773
Denominator for diluted net income (loss) per common share—adjusted weighted average shares	118,713	119,215	114,525	119,543
Basic loss per common share (in dollars per share)	$ 0.01	$ 0.11	$ (0.13)	$ 0.08
Diluted loss per common share (in dollars per share)	$ 0.01	$ 0.10	$ (0.13)	$ 0.07
Employee Stock Option
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)			4,185