SCHEDULE I - Evoqua Water Technologies Corp. Condensed Statements of Changes in Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of net income to cash flows provided by operating activities:
Foreign currency exchange (gains) losses on intercompany loans and other non-cash items	$ (1,094)	$ (8,202)	$ 10,713
Changes in assets and liabilities
Accrued expenses and other liabilities	21,881	22,078	(9,159)
Prepaids and other current assets	260	2,088	9,447
Net cash provided by operating activities	178,705	177,026	125,196
Investing activities
Net cash (used in) provided by investing activities	(97,172)	11,992	(94,532)
Financing activities
Proceeds from issuance of common stock	21,205	10,091	363
Taxes paid related to net share settlements of share-based compensation awards	(1,323)	(9,832)	(1,270)
Net cash (used in) provided by financing activities	(130,344)	(108,117)	5,744
Change in cash and cash equivalents	(46,757)	83,120	27,516
Beginning of period		109,881	82,365
End of period			109,881
Parent Company
Condensed Financial Statements, Captions [Line Items]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(51,482)	(113,649)	9,523
Reconciliation of net income to cash flows provided by operating activities:
Net (loss) income of subsidiaries	(52,981)	(114,109)	9,293
Foreign currency exchange (gains) losses on intercompany loans and other non-cash items	0	(15)	0
Changes in assets and liabilities
Due from affiliates	(11,638)	5,842	0
Due to affiliates	0	(9,747)	1,343
Accrued expenses and other liabilities	0	160	0
Prepaids and other current assets	(36)	(24)	(161)
Net cash provided by operating activities	(13,173)	(4,244)	952
Investing activities
Contributed capital	0	0	0
Net cash (used in) provided by investing activities	0	0	0
Financing activities
Proceeds from issuance of common stock	21,205	18,927	363
Taxes paid related to net share settlements of share-based compensation awards	(1,323)	(9,832)	(1,270)
Net cash (used in) provided by financing activities	19,882	9,095	(907)
Change in cash and cash equivalents	6,709	4,851	45
Beginning of period	4,972	121	76
End of period	$ 11,681	$ 4,972	$ 121

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