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                                                                     Exhibit 4.1

NOTE MODIFICATION AGREEMENT AND AMENDMENT TO LOAN AGREEMENT DATED JUNE 20, 2003
  BETWEEN JPMORGAN CHASE BANK, N.A. AND THE BADGER METER EMPLOYEE SAVINGS AND
             STOCK OWNERSHIP PLAN AND TRUST, DATED APRIL 18, 2005.

                AMENDMENT TO LOAN AGREEMENT DATED JUNE 20, 2003

This agreement is dated as of April 18, 2005, by and between Badger Meter
Employee Savings and Stock Ownership Plan and Trust (the "Borrower") and
JPMorgan Chase Bank, N.A., successor by merger to Bank One, NA with its main
office in Chicago, IL (the "Bank"), and its successors and assigns.

WHEREAS, the Borrower and the Bank entered into a Loan Agreement dated June 20,
2003, as amended (if applicable) (the "Credit Agreement"); and

WHEREAS, the Borrower has requested and the Bank has agreed to amend the Credit
Agreement as set forth below;

NOW, THEREFORE, in mutual consideration of the agreements contained herein and
for other good and valuable consideration, the parties agree as follows;

1.    DEFINED TERMS. Capitalized terms not defined herein shall have the meaning
      ascribed in the Credit Agreement.

2.    MODIFICATION OF CREDIT AGREEMENT. The Credit Agreement is hereby amended
      as follows:

      2.1   Section 1.13 of the Credit Agreement captioned "Termination Date"
            and Section 2.1 of the Credit Agreement captioned "Stock Acquisition
            Loan" are hereby amended by deleting the date "April 30, 2006"
            contained therein and replacing it with "April 30, 2008".

3.    RATIFICATION. The Borrower confirms that the Credit Agreement remains in
      full force and effect, other than as specifically modified herein.

4.    EXECUTION AND DELIVERY. This agreement shall become effective only after
      it is fully executed by the Borrower, Badger Meter, Inc., and the Bank,
      and the Bank shall have received from the Borrower the following
      documents: Note Modification Agreement.

5.    ACKNOWLEDGEMENT OF BORROWER. The Borrower, the Bank and Badger Meter, Inc.
      acknowledge and agree that this agreement is limited to the terms outlined
      above, and shall not be construed as an agreement to change any other
      terms or provisions of the Credit Agreement. This agreement shall not
      establish a course of dealing or be construed as evidence of any
      willingness on the Bank's part to grant other or future agreements, should
      any be requested.

6.    NOT A NOVATION. This agreement is a modification only and not a novation.
      Except for the above-quoted modification(s), the Credit Agreement, any
      loan agreements, credit agreements, reimbursement agreements, security
      agreements, mortgages, deeds of trust, pledge agreements, assignments,
      guaranties, instruments or documents executed in connection with the
      Credit Agreement, and all the terms and conditions thereof, shall be and
      remain in full force and effect with the changes herein deemed to be
      incorporated therein. This agreement is to be considered attached to the
      Credit Agreement and made a part thereof. This agreement shall not release
      or affect the liability of any guarantor of any promissory note or credit
      facility executed in reference to the Credit Agreement or release any
      owner of collateral granted as security for the Credit Agreement. The
      validity, priority and enforceability of the Credit Agreement shall not be
      impaired hereby. To the extent that any provision of this agreement
      conflicts with any term or condition set forth in the Credit Agreement, or
      any document executed in conjunction therewith, the provisions of this
      agreement shall supersede and control. The Borrower and the Bank,
      respectfully, each expressly reserves all rights against all parties to
      the Credit Agreement.

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BANK:

JPMORGAN CHASE BANK, N.A.

By: /s/ Gregory S. Dorf, Senior Vice President
    -------------------------------------------

Date Signed: 5/16/05

BORROWER:  BADGER METER EMPLOYEE SAVINGS AND STOCK OWNERSHIP PLAN AND TRUST

By: /s/ Michael C. Wieber,
    ------------------------------------
    Vice President, Marshall & Ilsley Trust Company N.A., Trustee

Date Signed: 5/12/05

By: /s/ Lora C. Sykora,
    ------------------------------------
   Vice President, Marshall & Ilsley Trust Company N.A., Trustee

Date Signed: 5/12/05

The undersigned, Badger Meter, Inc., is signing below to acknowledge, ratify,
and reaffirm the representation, warranties and convenants set forth in Sections
3, 5, and 7 of the Loan Agreement dated June 20, 2003.

BADGER METER, INC.

BY: /s/ Richard Johnson, CFO & Treasurer
    -----------------------------------------

Date Signed: 4/18/05

                                                     NOTE MODIFICATION AGREEMENT

This agreement is dated as of April 19, 2005 (the "Agreement Date"), to be
effective as of April 19, 2005 (the "Effective Date"), by and between Badger
Meter Employee Savings and Stock Ownership Plan and Trust (the "Borrower") and
JP Morgan Chase Bank, NA, successor by merger to Bank One, NA with its main
office in Chicago, IL (the "Bank").

WHEREAS, the Borrower executed a Promissory Note as evidence of indebtedness in
the original face amount of One Million Two Hundred Eight-Five Thousand and
00/100 Dollars ($1,285,000.00), dated June 20, 2003 owing by the Borrower to the
Bank, as same may have been amended or modified from time to time (the "Note"),
which Note has at all times been, an is now, continuously and without
interruption outstanding in favor of the Bank; and,

WHEREAS, the Borrower has requested and the Bank has agreed that the Note be
modified to the limited extent as hereinafter set forth;

NOW THEREFORE, in mutual consideration of the agreements contained herein and
for other good and valuable consideration, the parties agree as follows:

1.    ACCURARY OF RECITALS. The Borrower acknowledges the accuracy of the
      Recitals stated above.

2.    MODIFICATION OF NOTE.

      2.1   From and after the Effective Date, the date in which the entire
            unpaid principal balance plus all accrued interest shall be due and
            payable is hereby changed from April 30, 2006 to April 30, 2008.

3. RATIFICATION OF RELATED DOCUMENTS AND COLLAERAL. The Note shall remain in
full force and effect as IT may be modified herein.

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4. EXECUTION AND DELIVERY OF AGREEMENT BY THE BANK. Neither the Borrower nor the
Bank shall be bound by this agreement until both the Borrower and the Bank have
executed this Agreement.

5. INTEGRATION, ENTIRE AGREEMENT, CHANGE, DISCHARGE, TERMINATION, OR WAIVER. The
Note as modified herein (along with the related Loan Agreement dated June 20,
2003, as amended, between JPMorgan Chase Bank, N.A., successor by merger to Bank
One, NA and Badger Meter Employee Savings and Stock Ownership Plan and Trust)
contain the complete understanding and agreement of the Borrower and the Bank in
respect of the loan and supersede all prior representations, warranties,
agreements, arrangements, understandings, and negotiations. No provision of the
Note as modified herein may be changed, discharged, supplemented, terminated, or
waived except in a writing signed by the party against whom it is being
enforced.

6. COUNTERPART EXECUTION. This agreement may be executed in multiple
counterparts, each of which, when so executed, shall be deemed an original, but
all such counterparts, taken together, shall constitute one and the same
agreement.

7. NOT A NOVATION. This agreement is a modification only and not a novation. In
addition to all amounts hereafter due under the Note as modified herein, all
accrued interest evidenced by the Note being modified by this agreement shall
continue to be due and payable until paid. Except for the above-quoted
modification(s), the Note, and all the terms and conditions thereof, shall be
and remain in full force and effect with the changes herein deemed to be
incorporated therein. This agreement is to be considered attached to the Note
and made a part thereof. This agreement shall not release or affect the
liability of any guarantor, surety or endorser of the Note or release any owner
of collateral securing the Note. The validity, priority and enforceability of
the Note shall not be impaired hereby.

BANK:

JPMORGAN CHASE BANK, N.A.

By: /s/ Gregory S. Dorf, Senior Vice President
    ---------------------------------------------

Date Signed: 5/16/05

BORROWER: BADGER METER EMPLOYEE SAVINGS AND STOCK OWNERSHIP PLAN AND TRUST

By: /s/ Michael C. Wieber,
    --------------------------------------------
    Vice President, Marshall & Ilsley Trust Company N.A., Trustee

Date Signed: 5/12/05

By: /s/ Lora C. Sykora,
    ------------------------------------------
    Vice President, Marshall & Ilsley Trust Company N.A., Trustee

Date Signed: 5/12/05

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