Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Numerator:
Numerator for basic and diluted earnings (loss) per common share—Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 53,145	$ (16,730)
Denominator:
Denominator for basic net income (loss) per common share—weighted average shares	115,465	113,950
Effect of dilutive securities:
Share‑based compensation	5,443	0
Denominator for diluted net income (loss) per common share—adjusted weighted average shares	120,908	113,950
Basic income (loss) per common share	$ 0.46	$ (0.15)
Diluted income (loss) per common share	$ 0.44	$ (0.15)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	4,168

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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