Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Numerator for basic and diluted earnings (loss) per common share—Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 21,384	$ 4,135	$ 82,341	$ (11,211)
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	116,621	114,653	116,621	114,653
Effect of dilutive securities:
Share‑based compensation	3,595	4,781	4,432	0
Denominator for diluted net income (loss) per common share—adjusted weighted average shares	120,216	119,434	121,053	114,653
Basic income (loss) per common share	$ 0.18	$ 0.04	$ 0.71	$ (0.10)
Diluted income (loss) per common share	$ 0.18	$ 0.03	$ 0.68	$ (0.10)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)				4,358