Earnings per share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Numerator:
Net income (loss) attributable to Evoqua Water Technologies Corp.	$ 31,308	$ 21,384	$ 7,812	$ 53,145	$ 1,688	$ 4,135	$ 1,384	$ (16,730)	$ 113,649	$ (9,523)	$ 6,135
Denominator:
Denominator for basic net income per common share—weighted average shares									116,721	114,703	113,944
Effect of dilutive securities:
Share‑based compensation									4,342	0	6,221
Denominator for diluted net loss per common share—adjusted weighted average shares									121,063	114,703	120,165
Basic income (loss) per common share	$ 0.26	$ 0.18	$ 0.07	$ 0.46	$ 0.01	$ 0.04	$ 0.01	$ (0.15)	$ 0.97	$ (0.08)	$ 0.05
Diluted income (loss) per common share	$ 0.26	$ 0.18	$ 0.06	$ 0.44	$ 0.01	$ 0.03	$ 0.01	$ (0.15)	$ 0.94	$ (0.08)	$ 0.05
Share-based Payment Arrangement, Option [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount										2,512