<PAGE>   1
                                                                Exhibit 10.1

                                 TENTH AMENDMENT
                                 ---------------

                  This Tenth Amendment (this "Amendment") is entered into as of
this 29th day of December, 2000 among Waterlink, Inc. (the "Company"), Bank of
America, N.A. (f/k/a Bank of America National Trust and Savings Association), as
Agent (the "Agent"), and the financial institutions from time to time party
thereto (the "Banks"). Unless otherwise specified herein, capitalized terms used
in this Amendment shall have the meanings ascribed to them by the Agreement (as
defined below).

                                    RECITALS
                                    --------

                  WHEREAS, the Company, the Agent and the Banks are party to
that certain Amended and Restated Credit Agreement, dated as of June 27, 1997
and as amended and restated as of February 11, 2000 (as amended, supplemented,
restated or otherwise modified from time to time, the "Agreement");

                  WHEREAS, the Company, the Agent and the Banks wish to enter
into certain amendments to the Agreement, each as more fully set forth herein;

                  NOW THEREFORE, in consideration of the mutual execution hereof
and other good and valuable consideration, the parties hereto agree as follows:

                  SECTION 1.        AMENDMENTS.

                  (a)      SECTION 1.01 OF THE AGREEMENT IS HEREBY AMENDED BY
INSERTING THE FOLLOWING DEFINITIONS IN APPROPRIATE ALPHABETICAL ORDER:

                  "C-TREAT NOTE DEFERRAL" shall mean that the obligees under the
         subordinated promissory notes listed on Annex A to the Tenth Amendment
         have agreed to a maturity date under each such subordinated promissory
         note occurring on or after April 15, 2001, such agreement to be in form
         and substance satisfactory to the Agent.

                  "SIGNIFICANT LINES OF BUSINESS" shall mean the three lines of
         business described as (i) the Company's Pure Water Division, (ii) the
         Company's Separations and the Company's European Water and Wastewater
         Divisions, and (iii) the Company's Specialty Products Division.

                  "TENTH AMENDMENT" means the Tenth Amendment to this Agreement,
         dated as of December 29, 2000.

                  "TENTH AMENDMENT EFFECTIVENESS DATE" means the date upon which
         the Agent advises the Company that the Tenth Amendment has become
         effective.

                  (b) THE DEFINITION OF "REVOLVING TERMINATION DATE" IN SECTION
1.01 OF THE AGREEMENT IS HEREBY AMENDED BY DELETING IT IN ITS ENTIRETY AND
INSERTING THE FOLLOWING IN LIEU THEREOF:

                  "REVOLVING TERMINATION DATE" means the earlier to occur of:


<PAGE>   2

                            (a) October 1, 2001; and

                            (b) the date on which the Revolving Loan Commitments
         terminate in accordance with the provisions of this Agreement.


                  (c) THE DEFINITION OF "TERM MATURITY DATE" IN SECTION 1.01 OF
THE AGREEMENT IS HEREBY AMENDED BY DELETING IT IN ITS ENTIRETY AND INSERTING THE
FOLLOWING IN LIEU THEREOF:

                  "TERM MATURITY DATE" means October 1, 2001.


                  (d) CLAUSE (a)(i) OF SECTION 2.10 OF THE AGREEMENT IS HEREBY
AMENDED BY DELETING IT IN ITS ENTIRETY AND REPLACING IT WITH THE FOLLOWING IN
LIEU THEREOF:

                  "(a) (i) TERM LOANS. On each date set forth below, the Company
         shall be required to repay the principal amount (or such other amount
         after giving effect to any prepayments permitted or required pursuant
         to this Agreement) of the Term Loans as is set forth opposite such date
         (each, a "Scheduled Repayment"):

                           Date                      Amount
                           ----                      ------

                  February 22, 2001                  2,000,000
                  March 30, 2001                     2,000,000
                  June 29, 2001                      2,000,000
                  Term Maturity Date                37,835,816.30;

                  PROVIDED, HOWEVER, that if the Company obtains the C-Treat
Note Deferral, then the Scheduled Repayment due on February 22, 2001 shall be
reduced to zero and the Scheduled Repayment due on March 30, 2001 shall be
increased to $4,000,000.".

                  (e) CLAUSE (c) OF SECTION 2.12 OF THE AGREEMENT IS HEREBY
AMENDED BY DELETING IT IN ITS ENTIRETY AND REPLACING IT WITH THE FOLLOWING IN
LIEU THEREOF:

                            (c) PREPAYMENT FEE. The Company shall pay to the
         Agent, for distribution to each Bank based on its Pro Rata Share of the
         Term Loans, a prepayment fee ("Prepayment Fee") in an aggregate amount
         equal to 1.40% of the amount of any prepayment of Term Loans pursuant
         to SECTION 2.08 or 2.09. Such Prepayment Fee shall be due and payable
         upon the date of any such prepayment of Term Loans.".

                  (f) SECTION 8.05 OF THE AGREEMENT IS HEREBY AMENDED BY
REPLACING THE PERIOD AT THE END OF SUBCLAUSE (K) WITH A SEMICOLON FOLLOWED BY
THE WORD "AND", AND ADDING THE FOLLOWING SUBCLAUSE (L) THERETO:

                  "(l) Subordinated Indebtedness to be incurred after the Tenth
         Amendment Effectiveness Date in an amount not to exceed $1,000,000 in
         gross cash proceeds on terms and conditions and in form and substance
         satisfactory to the Agent."

                                       2
<PAGE>   3

                  (g) SECTION 9.01 OF THE AGREEMENT IS HEREBY AMENDED BY
REPLACING THE PERIOD AT THE END OF SUBCLAUSE (O) WITH A SEMICOLON FOLLOWED BY
THE WORD "OR", AND ADDING THE FOLLOWING SUBCLAUSES (P) AND (Q) THERETO:

                  "(p) ASSET OR STOCK DISPOSITION. The Company shall not (i)
         have entered into a purchase agreement for either (A) the sale of stock
         of at least one of the Significant Lines of Business on or prior to
         January 19, 2001 or (B) the sale of all or substantially all of the
         assets of at least one of the Significant Lines of Business on or prior
         to January 25, 2001, or (ii) have entered into a purchase agreement for
         the sale of at least two of the Significant Lines of Business on or
         prior to January 31, 2001, or (iii) have delivered to its shareholders
         a request for approval on or prior to March 1, 2001, if required by
         applicable law in connection with the sale of any Significant Lines of
         Business as referred to in (i) and (ii) above (the Banks acknowledge
         and agree that notwithstanding the requirements of SECTION 8.02 of the
         Agreement, the Company is permitted to enter into such agreements
         identified in clauses (i), (ii) and (iii) of this paragraph and such
         action shall not be a default or Event of Default under this Section
         9.01); or

                  (q) SUBORDINATED INDEBTEDNESS The Company shall not have
         received $1,000,000 in gross cash proceeds from Subordinated
         Indebtedness after the Tenth Amendment Effectiveness Date and before
         February 22, 2001 on terms and conditions and in form and substance
         satisfactory to the Agent."

                  SECTION 2. WAIVER. Notwithstanding the requirements of
SECTIONS 8.15, 8.17, 8.18 and 8.19 of the Agreement, the Banks hereby (i) waive
compliance by the Company with the requirements of said SECTION 8.19, for each
period ending on or prior to November 30, 2000, and (ii) waive compliance by the
Company with the requirements of said SECTIONS 8.15, 8.17 and 8.18 of the
Agreement for each period ending on or prior to February 22, 2001; PROVIDED,
HOWEVER, that such waiver contained in this Section 2(ii) shall be applicable to
the periods ending prior to March 31, 2001, in the event that the Company
obtains the C-Treat Note Deferral; PROVIDED, FURTHER, that such waivers
contained in this Section 2 shall be immediately withdrawn on the date upon
which EBIT of the Company, as reported in the monthly financial information
package delivered to the Banks no later than the 30th day of each calendar month
pursuant to SECTION 7.01(C) of the Agreement relating to the immediately
preceding calendar month, is less than:

               (i) $500,000 for the period from October 1, 2000 to and including
          December 31, 2000;

               (ii) $750,000 for the period from October 1, 2000 to and
          including January 31, 2001;

               (iii) $1,518,000 for the period from October 1, 2000 to and
          including February 28, 2001; and

               (iv) $2,949,000 for the period from October 1, 2000 to and
          including March 31, 2001;

                                       3
<PAGE>   4

         and; PROVIDED, FURTHER, that any amendment to this Section 2 shall
require the consent of each Bank.

                  SECTION 3.        REFERENCE TO AND EFFECT UPON THE AGREEMENT.

                  (a) Except as specifically amended above, the Agreement shall
remain in full force and effect and is hereby ratified and confirmed.

                  (b) The execution, delivery and effectiveness of this
Amendment shall not operate as a waiver of any right, power or remedy of the
Bank under the Agreement, nor constitute a waiver of any provision of the
Agreement, except as specifically set forth herein. Upon the effectiveness of
this Amendment, each reference in the Agreement to "this Agreement",
"hereunder", "hereof", "herein" or words of similar import shall mean and be a
reference to the Agreement as amended hereby.

                  SECTION 4.        GOVERNING  LAW. THIS  AMENDMENT  SHALL BE
GOVERNED BY AND  CONSTRUED IN  ACCORDANCE  WITH THE INTERNAL LAWS OF THE
STATE OF ILLINOIS.

                  SECTION 5.        HEADINGS.  Section  headings  in this
Amendment  are  included  herein  for  convenience  of reference only and shall
not constitute a part of this Amendment for any other purposes.

                  SECTION 6.        COUNTERPARTS.  This  Amendment  may be
executed in any number of counterparts (including by facsimile transmission),
each of which when so executed shall be deemed an original but all such
counterparts shall constitute one and the same instrument.

                  SECTION 7. EFFECTIVENESS. This Amendment shall become
effective as of the date first written above upon the delivery to the Agent of
executed signature pages (including by facsimile transmission) to this Amendment
signed by the Company and the Banks.

                            [signature pages follow]

                                       4
<PAGE>   5



         IN WITNESS WHEREOF, the parties hereto have executed this Amendment by
its duly authorized officer as of the date first written above.

                              WATERLINK, INC.


                              By: /s/ Mark E. Brody
                                  --------------------------------------------

                              Title: Chief Financial Officer
                                     -----------------------------------------


                              BANK OF AMERICA, N.A., as Agent


                              By: /s/ Kristine D. Hyde
                                  --------------------------------------------

                              Title: Vice President
                                     -----------------------------------------


                              BANK OF AMERICA, N.A., Individually as a Bank


                              By: /s/ Jennifer L. Gerdes
                                  --------------------------------------------

                              Title: Vice President
                                     -----------------------------------------


                              COMERICA BANK


                              By: /s/ Preeti Sarnaik
                                  --------------------------------------------

                              Title: Assistant Vice President
                                     -----------------------------------------


                              FIFTH THIRD BANK, CENTRAL OHIO


                              By: /s/ Stephen S. Brooks
                                  --------------------------------------------

                              Title: Vice President
                                     -----------------------------------------


                                     S-1

                             [TO TENTH AMENDMENT]
<PAGE>   6
                              HARRIS TRUST AND SAVINGS BANK


                              By: /s/ Michael J. Johnson
                                  --------------------------------------------

                              Title: Vice President
                                     -----------------------------------------


                              PNC BANK, NATIONAL ASSOCIATION


                              By: /s/ Robert G. Radermacher
                                  --------------------------------------------

                              Title: Senior Vice President
                                     -----------------------------------------


                              UNION BANK OF CALIFORNIA, N.A.


                              By: /s/ Christiana Creekpaum
                                  --------------------------------------------

                              Title:  Vice President
                                      ----------------------------------------



                                     S-2

                             [TO TENTH AMENDMENT]