<PAGE>

                                EXHIBIT 10.13E
                                --------------

                              FIFTH AMENDMENT TO
                              ------------------
                               CREDIT AGREEMENT
                               ----------------

          THIS FIFTH AMENDMENT TO AMENDED AND RESTATED CREDIT AGREEMENT (the
"Amendment"), dated as of March 9, 2001 is entered into between MELLON BANK,
 ---------
N.A., a national association ("Bank"), and SOUTHWEST WATER COMPANY, a Delaware
                               ----
corporation ("Borrower").
              --------

                                   RECITALS
                                   --------

          A.   Borrower and Bank have previously entered into that certain
Amended and Restated Credit Agreement dated as of December 23, 1997, as amended
by that certain First Amendment to Amended and Restated Credit Agreement dated
as of September 1, 1998, that certain Second Amendment to Amended and Restated
Credit Agreement dated as of September 29, 1999 and that certain Third Amendment
to Amended and Restated Credit Agreement dated as of July 19, 2000, and that
certain Fourth Amendment to Amended and Restated Credit Agreement dated as of
September 29, 2000 (collectively, the "Credit Agreement"), pursuant to which
                                       ----------------
Bank has made certain loans and financial accommodations available to Borrower.
Terms used herein without definition shall have the meanings ascribed to them in
the Credit Agreement.

          B.   Bank and Borrower wish to amend the Credit Agreement under the
terms and conditions set forth in this Amendment. Borrower is entering into this
Amendment with the understanding and agreement that, except as specifically
provided herein, none of Bank's rights or remedies as set forth in the Credit
Agreement is being waived or modified by the terms of this Amendment.

          NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants herein contained, and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereby
agree as follows:

     1.     Amendments to Credit Agreement
            ------------------------------

          (a)  The definition of "Revolving Commitment" set forth in Section
                                  --------------------
1.01 of the Credit Agreement is hereby amended and restated in its entirety to
read as follows:

                                  "`Revolving Commitment': The amount of
                                    --------------------
                           $7,000,000 as such amount may be reduced pursuant to
                           Section 2.01(C); provided however, that such amount
                                            ----------------
                           shall be increased to $9,000,000 for a period
                           beginning on March 9, 2001 and ending on August 1,
                           2001."

          (b)  Clause (v) of Section 6.02(f) of the Credit Agreement is hereby
amended and restated in their entirety to read as follows:
<PAGE>

                           "(v) unsecured funded bank debt not to exceed an
                           aggregate of $26,000,000 at any time (including,
                           without limitation, unsecured funded bank debt
                           incurred pursuant to the Loan Documents and the
                           Suburban Loan Documents and unsecured funded bank
                           debt to Bank of America as described in clause (iii)
                           above); provided however, that such amount shall be
                                   ----------------
                           increased to $30,000,000 for a period beginning on
                           March 9, 2001 and ending on August 1, 2001."

               2.        Effectiveness of this Amendment. Bank must have
                         -------------------------------
received the following items, in form and content acceptable to Bank, before
this Amendment is effective and before Bank is required to extend any credit to
Borrower as provided for by this Amendment.

                    (a)    Amendment. This Amendment fully executed in a
                           ---------
sufficient number of counterparts for distribution to Bank and Borrower.

                    (b)    Amendment Fee. Receipt by Bank of the amendment fee
                           -------------
set forth in Paragraph 3 below.

                    (c)    Acceptance Letter. An acceptance letter from the El
                           -----------------
Paso County Water Authority, in form and content acceptable to Bank.

                    (d)    Note. The Fourth Amended and Restated Promissory
                           ----
Note, the form of which is attached hereto as Exhibit A, fully executed by the
Borrower.

                    (d)    Authorizations. Evidence that the execution, delivery
                           --------------
and performance by Borrower and each guarantor or subordinating creditor of this
Amendment and any instrument or agreement required under this Amendment have
been duly authorized.

                    (e)    Representations and Warranties. The representations
                           ------------------------------
and warranties set forth in the Credit Agreement must be true and correct.

                    (f)    Bank of America, N.A. and Borrower Amendment.
                           --------------------------------------------
Execution and delivery to Bank of the Bank of America, N.A. and Borrower
Amendment, which includes the same amendments contained in this Amendment.

                    (g)    Other Required Documentation. All other documents and
                           ----------------------------
legal matters in connection with the transactions contemplated by this Amendment
shall have been delivered or executed or recorded and shall be in form and
substance satisfactory to Bank.

               3.        Amendment Fee. Borrower shall pay to Bank a renewal fee
                         -------------
in the amount of $____________________ for the processing and approval of this
Amendment, which fee will be fully earned on the date of this Amendment.

               4.        Representations and Warranties. The Borrower represents
                         ------------------------------
and warrants as follows:
<PAGE>

               (a)   Authority. The Borrower has the requisite corporate power
                     ---------
and authority to execute and deliver this Amendment and to perform its
obligations hereunder and under the Loan Documents (as amended or modified
hereby) to which it is a party. The execution, delivery and performance by the
Borrower of this Amendment and the performance by Borrower of each Loan Document
(as amended or modified hereby) to which it is a party have been duly approved
by all necessary corporate action of Borrower and no other corporate proceedings
on the part of Borrower are necessary to consummate such transactions.

               (b)   Enforceability. This Amendment has been duly executed and
                     --------------
delivered by the Borrower. This Amendment and each Loan Document (as amended or
modified hereby) is the legal, valid and binding obligation of Borrower,
enforceable against Borrower in accordance with its terms, and is in full force
and effect.

               (c)   Representations and Warranties. The representations and
                     ------------------------------
warranties contained in each Loan Document (other than any such representations
or warranties that, by their terms, are specifically made as of a date other
than the date hereof) are correct on and as of the date hereof as though made on
and as of the date hereof.

               (d)   No Default. No event has occurred and is continuing that
                     ----------
constitutes an Event of Default.


          5.      Choice of Law. The validity of this Amendment, its
                  -------------
construction, interpretation and enforcement, the rights of the parties
hereunder, shall be determined under, governed by, and construed in accordance
with the internal laws of the State of California governing contracts only to be
performed in that State.

          6.      Counterparts. This Amendment may be executed in any number of
                  ------------
counterparts and by different parties in separate counterparts, each of which
when so executed and delivered, shall be deemed an original, and all of which,
when taken together, shall constitute one and the same instrument. Delivery of
an executed counterpart of a signature page to this Amendment by telefacsimile
shall be effective as delivery of a manually executed counterpart of this
Amendment or such Consent.

          7.      Due Execution. The execution, delivery and performance of this
                  -------------
Amendment are within the power of Borrower, have been duly authorized by all
necessary corporate action, have received all necessary governmental approvals,
if any, and do not contravene any law or any contractual restrictions binding on
Borrower.

          8.      Reference to and Effect on the Loan Documents.
                  ---------------------------------------------

               (a)   Upon and after the effectiveness of this Amendment, each
reference in the Credit Agreement to "this Agreement", "hereunder", "hereof" or
words of like import referring to the Credit Agreement, and each reference in
the other Loan Documents to "the Credit Agreement", "thereof" or words of like
import referring to the Credit Agreement, shall mean and be a reference to the
Credit Agreement as modified and amended hereby.

               (b)   Except as specifically amended above, the Credit Agreement
and all other Loan Documents, are and shall continue to be in full force and
effect and are hereby in all
<PAGE>

respects ratified and confirmed and shall constitute the legal, valid, binding
and enforceable obligations of Borrower to Bank.

               (c)    The execution, delivery and effectiveness of this
Amendment shall not, except as expressly provided herein, operate as a waiver of
any right, power or remedy of Bank under any of the Loan Documents, nor
constitute a waiver of any provision of any of the Loan Documents.

               (d)    To the extent that any terms and conditions in any of the
Loan Documents shall contradict or be in conflict with any terms or conditions
of the Credit Agreement, after giving effect to this Amendment, such terms and
conditions are hereby deemed modified or amended accordingly to reflect the
terms and conditions of the Credit Agreement as modified or amended hereby.

          9.     Ratification. Borrower hereby restates, ratifies and reaffirms
                 ------------
each and every term and condition set forth in the Credit Agreement, as amended
hereby, and the Loan Documents effective as of the date hereof.

          10.    Estoppel. To induce Bank to enter into this Amendment and to
                 --------
continue to make advances to Borrower under the Credit Agreement, Borrower
hereby acknowledges and agrees that, after giving effect to this Amendment, as
of the date hereof, there exists no Event of Default and no right of offset,
defense, counterclaim or objection in favor of Borrower as against Bank with
respect to the Obligations.

               IN WITNESS WHEREOF, the parties have entered into this Amendment
as of the date first above written.

"Bank"                                        "Borrower"

MELLON BANK, N.A.                             SOUTHWEST WATER COMPANY,
a national association                        a Delaware corporation

By:  /s/ GARRY HANDLEMAN                      By:  /s/ THOMAS C. TEKULVE
     -------------------                           ---------------------
Name:   Garry Handelman                       Name:   Thomas C. Tekulve
Title:  Vice President                        Title:  Vice President - Finance


                                              By  /s/ PETER J. MOERBEEK
                                                -----------------------
                                              Name:   Peter J. Moerbeek,
                                              Title:  Chief Financial Officer
<PAGE>



                                  EXHIBIT "A"
                                  -----------

                            SOUTHWEST WATER COMPANY

                          THIRD AMENDED AND RESTATED
                                PROMISSORY NOTE

$9,000,000.00                                                     March 9, 2001
                                                        West Covina, California

          FOR VALUE RECEIVED, SOUTHWEST WATER COMPANY, a Delaware corporation
(the "Borrower"), promises to pay to the order of MELLON BANK, N.A. (the "Bank")
      --------                                                            ----
on the Maturity Date (as defined in the Credit Agreement referred to below) the
principal amount of Nine Million Dollars ($9,000,000.00), or, if less, the
aggregate amount of Revolving Loans (as defined in the Credit Agreement referred
to below) made by the Bank to the Borrower pursuant to the Credit Agreement
referred to below outstanding on the Maturity Date.

          The Borrower also promises to pay interest on the unpaid principal
amount hereof from the date hereof until paid at the rates and at the times
which shall be determined in accordance with the provisions of the Credit
Agreement.

          All unpaid amounts of principal and interest shall be due and payable
in full on the Maturity Date.

          All payments of principal and interest in respect of this Note
shall be made in lawful money of the United States of America in same day funds
at the office of the Bank located at Three Mellon Bank Center, 23rd Floor/Loan
Administration, Pittsburgh, Pennsylvania 15259 or at such other place as shall
be designated in writing for such purpose in accordance with the terms of the
Credit Agreement. Until notified of the transfer of this Note, the Borrower
shall be entitled to deem the Bank or such person who has been so identified by
the transferor in writing to the Borrower as the holder of this Note, as the
owner and holder of this Note. Each of the Bank and any subsequent holder of
this Note agrees that before disposing of this Note or any part hereof, it will
make a notation hereon of all principal payments previously made hereunder and
of the date to which interest hereon has been paid on the schedule attached
hereto, if any; provided, however, that the failure to make notation of any
                --------  -------
payment made on this Note shall not limit or otherwise affect the obligation of
the Borrower hereunder with respect to payments of principal or interest on this
Note.

          This Note is referred to in, and is entitled to the benefits of, the
Amended and Restated Credit Agreement dated as of December 23, 1997, as amended
from time to time (the "Credit Agreement") between the Borrower and the Bank.
                        ----------------
The Credit Agreement, among other things, (i) provides for the making of
advances (the "Loans") by the Bank to the Borrower from time to time in an
               -----
aggregate amount not to exceed at any time outstanding the U.S. dollar amount
<PAGE>

first above mentioned, the indebtedness of the Borrower resulting from each such
Loan being evidenced by this Note, and (ii) contains provisions for acceleration
of the maturity hereof upon the happening of certain stated events and also for
prepayments on account of principal hereof prior to the maturity hereof upon the
terms and conditions therein specified.

          The terms of this Note are subject to amendment only in the manner
provided in the Credit Agreement.

          No reference herein to the Credit Agreement and no provision of this
Note or the Credit Agreement shall alter or impair the obligation of the
Borrower, which is absolute and unconditional, to pay the principal of and
interest on this Note at the place, at the respective times, and in the currency
herein prescribed.

          The Borrower promises to pay all costs and expenses, including
reasonable attorneys' fees, incurred in the collection and enforcement of this
Note. The Borrower hereby consents to renewals and extensions of time at or
after the maturity hereof, without notice, and hereby waives diligence,
presentment, protest, demand and notice of every kind and, to the full extent
permitted by law, the right to plead any statute of limitations as a defense to
any demand hereunder.

          This Note amends and restates in its entirety that certain Amended and
Restated Promissory Note dated as of July 19, 2000 in the amount of Seven
Million Dollars ($7,000,000) made by Borrower payable to the order of Bank
pursuant to the Credit Agreement.

          IN WITNESS WHEREOF, the Borrower has caused this Notice to be executed
and delivered by its duly authorized officers, as of the date and the place
first above-written.

                                               SOUTHWEST WATER COMPANY


                                               By:
                                                  ---------------------
                                               Name:    Thomas C. Tekulve
                                               Title:   Vice President - Finance



                                               By:
                                                   ---------------------
                                               Name:    Peter J. Moerbeek
                                               Title:   Vice President and
                                                        Chief Financial Officer
<PAGE>

                                  TRANSACTIONS
                                       ON
                                      NOTE

<TABLE>
<CAPTION>
Amount of            Amount of                                  Interest Paid     Principal     Notation
Loan Made            Principal Paid       Interest Paid         Through           Balance       Made By
---------            --------------       -------------         -------           -------       -------
<S>                  <C>                  <C>                   <C>               <C>           <C>
</TABLE>