Earnings per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Numerator:
Numerator for basic and diluted earnings per common share—Net income attributable to Evoqua Water Technologies Corp.	$ 6,433	$ 53,145
Denominator:
Denominator for basic net income per common share—weighted average shares	117,768	115,586
Effect of dilutive securities:
Share‑based compensation	3,790	5,443
Denominator for diluted net income per common share—adjusted weighted average shares	121,558	121,029
Basic income per common share	$ 0.05	$ 0.46
Diluted income per common share	$ 0.05	$ 0.44