<PAGE>
                                                                   Exhibit (4.0)

                             REVOLVING BUSINESS NOTE
                                    M&I BANK


BADGER METER. INC.               DECEMBER 29, 2003                $20.000.000.00
------------------               -----------------                --------------
Customer                         Date                             Amount


The undersigned ("Customer", whether one or more) promises to pay to the order
of M&I Marshall & Ilsley Bank ("Lender") at 770 North Water Street, Milwaukee,
Wisconsin 53202, the principal sum of $20.000.000.00 or, if less, the aggregate
unpaid principal amount of all loans made under this Note, plus interest, as set
forth below.

Lender will disburse loan proceeds to Customer's deposit account number
___[omitted]___or by other means acceptable to Lender.

Interest is payable on JANUARY 30, 2004, and on the same date of each
consecutive month thereafter and at maturity.

Principal is payable APRIL 30, 2004.

This Note bears interest on the unpaid principal balance before maturity
(whether upon demand, acceleration or otherwise) at the rates set forth on
Exhibit A attached hereto.

Interest is computed on the basis of a 360-day year on the actual number of days
principal is unpaid. Unpaid principal and interest bear interest after maturity
(whether by acceleration or lapse of time) until paid at the prime rate of
interest adopted by Lender as its base rate determinations from time to time
which may or may not be the lowest rate charged by Lender ("Prime Rate") (with
the rate changing as and when that Prime Rate changes) plus 3%.

If any payment is not paid when due, if a default occurs under any other
obligation of any Customer to Lender or if Lender deems itself insecure, the
unpaid balance shall, at the option of Lender, and without notice mature and
become immediately payable. The unpaid balance shall automatically mature and
become immediately payable in the event any Customer, surety, or guarantor
becomes the subject of bankruptcy or other insolvency proceedings. Lender's
receipt of any payment on this Note after the occurrence of an event of default
shall not constitute a waiver of the default or Lender's rights and remedies
upon such default.

The acceptance of this Note, the making of any loan, or any other action of
Lender does not constitute an obligation or commitment of Lender to make loans;
and any loans may be made solely in the discretion of Lender. This Note may be
prepaid in full or in part without penalty.

Lender is authorized to automatically charge payments due under this Note to
account number ___[omitted]___ at M&I Marshall & Ilsley Bank (See reverse side
regarding Notice of Transfers Varying in Amount.)

____ check here only if this Note is to be secured by a first lien mortgage or
equivalent security interest on a one-to-four family dwelling used as Customer's
principal place of residence.

This Note includes additional provisions on reverse side.

BADGER METER, INC.

                                                4545 W. BROWN DEER ROAD
                                                Street Address
                                                Milwaukee. WI 53223
                                                City/State/Zip


By: /s/ Richard A. Meeusen
    ----------------------------------------


By: /s/ Richard E. Johnson
    ----------------------------------------


                                       43
<PAGE>

                              ADDITIONAL PROVISIONS

This Note is secured by all existing and future security agreements, assignments
and mortgages between Lender and Customer, between Lender and any guarantor of
this Note, and between Lender and any other person providing collateral security
for Customer's obligations, and payment may be accelerated according to any of
them. Unless a lien would be prohibited by law or would render a nontaxable
account taxable, Customer grants to Lender a security interest and lien in any
deposit account Customer may at any time have with Lender. Lender may, at any
time after an occurrence of an event of default, without notice or demand,
setoff against any deposit balances or other money now or hereafter owed any
Customer by Lender any amount unpaid under this Note.

Lender is authorized to make book entries evidencing loans and payments and the
aggregate of all loans as evidenced by those entries is presumptive evidence
that those amounts are outstanding and unpaid to Lender. Customer covenants that
all loans shall be used solely for business and not personal purposes.

Customer agrees to pay all costs of administration and collection before and
after judgment, including reasonable attorneys' fees (including those incurred
in successful defense or settlement of any counterclaim brought by Customer or
incident to any action or proceeding involving Customer brought pursuant to the
United States Bankruptcy Code) and waives presentment, protest, demand and
notice of dishonor. Customer agrees to indemnify and hold harmless Lender, its
directors, officers, employees and agents, from and against any and all claims,
damages, judgments, penalties, and expenses, including reasonable attorneys'
fees, arising directly or indirectly from credit extended under this Note or the
activities of Customer. This indemnity shall survive payment of this Note.

Customer acknowledges that Lender has not made any representations or warranties
with respect to, and that Lender does not assume any responsibility to Customer
for, the collectability or enforceability of this Note or the financial
condition of any Customer. Customer authorizes Lender to disclose financial and
other information about Customer to others. Each Customer has independently
determined the collectability and enforceability of this Note.

Without affecting the liability of any Customer, surety, or guarantor, Lender
may, without notice, accept partial payments, release or impair any collateral
security for the payment of this Note or agree not to sue any party liable on
it. Without affecting the liability of any surety or guarantor, Lender may from
time to time, without notice, renew or extend the time for payment. The
obligations of all Customers under this Note are joint and several.

To the extent not prohibited by law, Customer consents that venue for any legal
proceeding relating to collection of this Note shall be, at Lender's option, the
county in which Lender has its principal office in this state, the county in
which any Customer resides or the county in which this Note was executed. This
Note shall be construed and enforced in accordance with the internal laws of
Wisconsin.

This Note is intended by Customer and Lender as a final expression of this Note
and as a complete and exclusive statement of its terms, there being no
conditions to the enforceability of this Note. This Note may not be supplemented
or modified except in writing, except as set forth in Exhibit A attached hereto.


                        PREAUTHORIZED TRANSFER DISCLOSURE

When Customer authorizes Lender to obtain payment of amounts becoming due Lender
by initiating charges to Customer's account, Customer also requests and
authorizes remitting financial institution to alert and honor same and to charge
same to Customer's account. This authorization will remain in effect until
Customer notifies Lender and the remitting financial institution in writing to
terminate this authorization and Lender and remitting financial institution have
a reasonable time to act on the termination. NOTICE OF TRANSFERS VARYING IN
AMOUNT: If Lender and remitting financial institution are not the same, Customer
is an individual, the account was established primarily for personal, family or
household purposes and the regular payments may vary in amount, Customer has the
right to receive a notice from Lender 10 days before each payment of how much
the payment will be; however, by signing this Note, Customer elects to receive
notice only when current payment would differ by more than 100% from previous
payment.


                      EXHIBIT A TO REVOLVING BUSINESS NOTE

This Note bears interest on the unpaid principal balance before maturity
(whether upon demand, acceleration or otherwise) at an annual rate equal to the
Adjusted Interbank Rate (as defined below) plus 75 basis points, which rate will
change as of


                                       44
<PAGE>

the first day of each calendar month. If the first day of any calendar month is
not a regular Business Day, the Adjusted Interbank Rate shall be established on
the preceding Business Day. "Business Day" shall mean any day other than a
Saturday, Sunday, public holiday or other day when commercial banks in Wisconsin
are authorized or required by law to close.

Customer may, from time to time and without premium or penalty, borrow and repay
the Loans in whole or in part; provided requests for advances or repayments
occur prior to 3:00 P.M. on any Business Day.

 "Adjusted Interbank Rate" means an annual rate for all loans evidenced by this
   Note (the "Loans") (rounded upwards, if necessary, to the nearest 1/100 of
               1%), determined pursuant to the following formula:

                 Adjusted Interbank Rate = Interbank Rate
                                           ----------------------
                                           1 - Interbank Reserve
                                           Requirement

"Interbank Rate" means with respect to any Loan, the rate per annum equal to the
rate (rounded upwards, if necessary, to the nearest 1/16 of 1%) quoted as the
rate at which dollar deposits in immediately available funds are offered on the
first day of each calendar month in the interbank Eurodollar market on or about
9:00 A.M., Milwaukee time, for a period of one (1) calendar month. If the first
day of any calendar month is not a regular Business Day, the Interbank Rate
shall be established on the preceding Business Day. Lender currently uses the
Reuters Information Service to provide information with respect to the interbank
Eurodollar market, but Lender may change the service providing such information
at any time. Each such determination shall be conclusive and binding upon the
parties hereto in the absence of demonstrable error.

"Interbank Reserve Requirement" means a percentage (expressed as a decimal)
equal to the aggregate reserve requirements in effect on the first day of each
calendar month (including all basic, supplemental, marginal and other reserves
and taking into account any transitional adjustments or other scheduled changes
in reserve requirements during each calendar month) specified for "Eurocurrency
Liabilities. Under Regulation D of the Board of Governors of the Federal Reserve
System, or any other regulation of the Board of Governors which prescribes
reserve requirements applicable to "Eurocurrency Liabilities" as presently
defined in Regulation D, as then in effect, as applicable to the class or
classes of banks of which Lender is a member. As of the date of this Note, the
Interbank Reserve Requirement is 0%.

INCREASED COSTS. If, Regulation D of the Board of Governors of the Federal
Reserve System, or the adoption of any applicable law, rule or regulation of
general application, or any change therein, or any interpretation or
administration thereof by any governmental authority, central bank or comparable
agency charged with the interpretation or administration thereof, or compliance
by Lender with any request or directive of general application (whether or not
having the force of law) of any such authority, central bank or comparable
agency:

          (a) shall subject Lender to any tax, duty or other charge with respect
to the Loans, the Note or its obligation to make Loans, or shall change the
basis of taxation of payments to Lender of the principal of or interest on the
Loans or any other amounts due under this Note in respect of the Loans or its
obligation to make Loans (except for changes in the rate of tax on the overall
net income of Lender); or

          (b) shall impose, modify or deem applicable any reserve (including,
without limitation, any reserve imposed by the Board of Governors of the Federal
Reserve System, but excluding any reserve included in the determination of
interest rates pursuant to this Note), special deposit or similar requirement
against assets of, deposits with or for the account of, or credit extended by,
Lender; or

          (c) shall affect the amount of capital required or expected to be
maintained by Lender or any corporation controlling Lender: or

          (d) shall impose on Lender any other condition affecting the Loans,
the Note or its obligation to make Loans;

and the result of any of the foregoing is to increase the cost to (or in the
case of Regulation D referred to above, to impose a cost on) Lender of making or
maintaining any Loans, or to reduce the amount of any sum received or receivable
by Lender under this Note with respect thereto, then within ten (10) days after
demand by Lender (which demand shall be accompanied by a statement setting forth
the basis of such demand), Customer shall pay directly to Lender such additional
amount or amounts as will compensate Lender for such increased cost or such
reduction. Determinations by Lender for purposes of this section of the effect
of any change in applicable laws or regulations or of any interpretations,
directives or requests thereunder on its costs of making or maintaining Loans or
sums receivable by it in respect of Loans,


                                       45
<PAGE>

and of the additional amounts required to compensate Lender in respect thereof,
shall be conclusive, absent manifest error.


DEPOSITS UNAVAILABLE OR INTEREST RATE UNASCERTAINABLE.

          (a) If Lender is advised that deposits in dollars (in the applicable
amount) are not being offered to banks in the relevant market for a period of
one (1) calendar month, or Lender otherwise determines (which determination
shall be binding and conclusive on all parties) that by reason of circumstances
affecting the interbank Eurodollar market adequate and reasonable means do not
exist for ascertaining the applicable Interbank Rate; or

          (b) If lenders similar to Lender have determined that the Interbank
Rate will not adequately and fairly reflect the cost to such lenders of
maintaining or funding loans based on the Interbank Rate, or that the making or
funding of such Interbank Rate loans has become impracticable as a result of an
event occurring after the date of this Note which in the opinion of Lender
materially affects such Interbank Rate loans;

then so long as such circumstances shall continue, Lender shall not be under any
obligation to make or continue Loans based on the Interbank Rate and on the
first Business Day of the next calendar month, such Loans shall bear interest at
the prime rate of interest adopted by Lender as its base rate for interest rate
determinations from time to time which mayor may not be the lowest rate charged
by Lender ("Prime Rate") (with the rate changing as and when that Prime Rate
changes) plus 0%. If such an agreement cannot be reached, such Loans shall be
repaid in full by Customer.

CHANGE IN LAW RENDERING INTERBANK RATE LOANS UNLAWFUL. In the event that any
change in (including the adoption of any new) applicable laws or regulations, or
any change in the interpretation of applicable laws or regulations by any
governmental or other regulatory body charged with the administration thereof,
should make it unlawful for any lender to make, maintain or fund Loans based on
the Interbank Rate, then: (a) Lender shall promptly notify Customer; (b) the
obligation of Lender to make or continue Loans based on the Interbank Rate shall
be suspended for the duration of such unlawfulness; and (c) on the first
Business Day of the following calendar month, such Loans shall bear interest at
the Prime Rate plus 0%, with the interest rate to change on each day that the
Prime Rate changes.

Dated as of December 29, 2003

Badger Meter, Inc.                        M&I Marshall & Ilsley Bank



By: /s/ Richard A. Meeusen                By: /s/ James P. McMullen
    ----------------------------------        ----------------------------------
                                              James P. McMullen, Vice President


By: /s/ Richard E. Johnson
    ----------------------------------


                                       46