<PAGE>

                                                                 Exhibit 10.13.6

                               SIXTH AMENDMENT TO
                          THE CONNECTICUT WATER COMPANY
                           EMPLOYEES' RETIREMENT PLAN

  (as amended and restated as of January 1, 1997, except as otherwise provided
                                    therein)

         1.       The following sentence is added to Section 2.15, as amended by
the Second Amendment, at the end thereof:

         "Notwithstanding anything to the contrary contained in Section 2.15,
Section 2.32, or elsewhere in the Plan, in no event shall any Employee of The
Unionville Water Company receive credit for Credited Service hereunder prior to
January 1, 2004."

         2.       The following sentence is added to Section 2.40 at the end
thereof:

         "In calculating an Employee's Vesting Service, service with The
Unionville Water Company, both before and after October 31, 2002, shall be taken
into account."

         3.       The following paragraph is added to Section 3.2, as amended by
the Second Amendment, at the end thereof:

         "Employees of The Unionville Water Company shall be eligible to
participate hereunder effective January 1, 2004, provided they have satisfied
the service requirements hereunder as of that date and are otherwise eligible to
participate hereunder. Service with The Unionville Water Company both before and
after October 31, 2002 shall count as Service for purposes of meeting the
eligibility requirements hereunder. In no event shall any Employee of The
Unionville Water Company receive credit for Credited Service hereunder prior to
January 1, 2004."

         4.       Section 4.2, as set forth in the Second Amendment, is amended
by the addition of the following unnumbered paragraph at the end thereof:

         "In the case of Participants who either (1) have not attained a Vested
Percentage of one hundred percent (100%) as of December 31, 2003, or (2) have
first become eligible to participate in this Plan after December 31, 2003, or
both, no more than thirty-seven and one half (37 1/2) years of Credited Service
shall be taken into account. This amendment to Section 4.2 is effective as of
January 1, 2004. In no event shall this change reduce the accrued benefit of any
Participant as of December 31, 2003."

         5.       Section 5.2 is amended to read as follows:

         "5.2     Early Commencement. A Participant who retires in accordance
with the provisions of Section 5.1 and elects to have payment of his Retirement
Income commence on his Early Retirement Date shall be entitled to receive a
reduced Annual Retirement Income in the form stated in Section 4.3. The amount
of such reduced Retirement Income shall equal (a) times (b) where:

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                  (a)      equals such Participant's Normal Retirement Income as
                           determined under Section 4.3 based on his Average
                           Earnings and his Credited Service as of his Early
                           Retirement Date and with the Actuarial Equivalent
                           factors described in Subsections 4.3(b) and 4.3 (c)
                           being determined as of his Early Retirement Date; and

                  (b)      (1) In the case of Participants who are Participants
                           as of December 31, 2003 and have attained a Vested
                           Percentage of one hundred percent (100%) as of
                           December 31, 2003, equals the appropriate percentage
                           factor from the following table:

<TABLE>
<CAPTION>
Complete Years by Which
Early Retirement Date
Precedes Normal                 Early Retirement
Retirement Date                Percentage Factors
-----------------------        ------------------
<S>                            <C>
          10                           .72
           9                           .76
           8                           .80
           7                           .84
           6                           .88
           5                           .92
           4                           .96
           3                          1.00
           2                          1.00
           1                          1.00
           0                          1.00
</TABLE>

                           (2) In the case of Participants who either (A) have
                           not attained a Vested Percentage of one hundred
                           percent (100%) as of December 31, 2003, or (B) first
                           become eligible to participate in this Plan after
                           December 31, 2003, or both, equals the appropriate
                           percentage factor from the following table:

<TABLE>
<CAPTION>
Complete Years by Which
Early Retirement Date
Precedes Normal                 Early Retirement
Retirement Date                Percentage Factors
-----------------------        ------------------
<S>                            <C>
          10                           .40
           9                          .46
           8                          .52
           7                          .58
           6                          .64
           5                          .70
           4                          .76
           3                          .82
           2                          .88
           1                           .94
           0                          1.00
</TABLE>

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                  (c)      This amendment to Section 5.2 is effective as of
                           January 1, 2004. In no event shall this change reduce
                           the amount of a Participant's benefit at Early
                           Retirement Date below the amount of the benefit that
                           the Participant would have been entitled to receive
                           based upon the early retirement factors set forth in
                           subparagraph (b)(1) of this Section 5.2, based upon
                           his accrued benefit under the Plan as of December 31,
                           2003."

         6.       Except as hereinabove modified and amended, the Plan as
amended shall remain in full force and effect.

         7.       This Amendment is effective as of January 1, 2004.

                                   CERTIFICATE

         The undersigned hereby certifies that The Connecticut Water Company
Employees' Retirement Plan, as amended and restated effective as of January 1,
1997, except as otherwise provided therein, was duly amended by the Board of
Directors of The Connecticut Water Company by a Sixth Amendment on November 12,
2003, and the Plan, as so amended, is in full force and effect.

November 12, 2003                         [ILLEGIBLE]
                                          -----------------------------
                                          Michele G. DiAcri
                                          Corporate Secretary

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