Accounting Policies (Policies)	12 Months Ended
Accounting Policies (Policies)	Sep. 30, 2021
Accounting Policies [Abstract]
Lessee, Leases	Leases The Company accounts for leases in accordance with ASC Topic No. 842, Leases. Lessee Accounting The Company leases office space, buildings, vehicles, forklifts, computers, copiers and other assets under non-cancelable operating and finance leases. The Company determines whether an arrangement is or contains a lease at the inception of the arrangement based on the terms and conditions in the contract. A contract contains a lease if there is an identified asset and the Company has the right to control the asset. If the arrangement contains a lease, the Company recognizes a right-of-use (“ROU”) asset and an operating lease liability as of the lease commencement date. Any lease arrangements with a term of 12 months or less are not recorded on the Consolidated Balance Sheets, and lease costs for these arrangements are recognized on a straight-line basis over the lease term. Many of the Company’s lease arrangements provide for an option to exercise one or more renewal terms or to terminate the lease arrangement. The Company includes these options when the Company is reasonably certain to exercise them in the leased term used to establish the ROU asset and lease liabilities. The discount rate utilized in calculating the lease liability is the rate implicit in the lease, if known, otherwise, the incremental borrowing rate (“IBR”) for the expected lease term is used. Operating lease assets and finance lease assets are included in Operating lease right-of-use assets, net and Property, plant, and equipment, net, respectively, on the Consolidated Balance Sheets. The corresponding operating lease liabilities are included in Accrued expenses and other liabilities and Obligation under operating leases on the Consolidated Balance Sheets. The corresponding finance lease liabilities are included in Accrued expenses and other liabilities and Other non‑current liabilities on the Consolidated Balance Sheets.
Lessor, Leases	Lessor Accounting The Company generates revenue through the lease of its water treatment equipment and systems to customers. In certain instances, the Company enters into a contract with a customer but must construct the underlying asset prior to its lease. At the time of contract inception, the Company determines if an arrangement is or contains a lease. These contracts generally contain both lease and non-lease components, including installation, maintenance, and monitoring services of the Company-owned equipment, in addition to sale of certain constructed assets. In situations where arrangements contain multiple elements, contract consideration is allocated based on relative standalone selling price. Lease components associated with underlying assets that have an alternative use are classified as operating leases with revenue recognized over time throughout the lease term. Lease components associated with underlying assets that have no alternative are classified as sales-type leases, with point in time revenue recognition at the on-set of the lease, or classified as financing transactions, with over time revenue recognition at the on-set of the construction of the underlying assets. In order for a component to be separate, the customer would be able to benefit from the right of use of the component separately or with other resources readily available to the customer and the right of the use is not highly dependent or highly interrelated with the other rights to use the other underlying assets or components.