Exhibit 10.10









                            IONICS, INCORPORATED
                   SUPPLEMENTAL EXECUTIVE RETIREMENT PLAN













































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                            IONICS, INCORPORATED
                   SUPPLEMENTAL EXECUTIVE RETIREMENT PLAN
                              TABLE OF CONTENTS

ARTICLE I   PURPOSE                                         1

ARTICLE 2   DEFINITIONS                                     2

    2.1     Account                                         2
    2.2     Actuary                                         2
    2.3     Additional Annuity Benefit                      2
    2.4     Beneficiary                                     3
    2.5     Benefit                                         3
    2.6     Board                                           3
    2.7     Cause                                           3
    2.8     Change of Control                               4
    2.9     Code                                            4
    2.10    Committee                                       5
    2.11    Company                                         5
    2.12    compensation                                    5
    2.13    Employment Termination                          5
    2.14    ERISA                                           5
    2.15    Executive                                       5
    2.16    Interest Rate                                   6
    2.17    Participant                                     6
    2.18    Pension Plan                                    6
    2.19    Pension Plan Amount                             6
    2.20    Plan                                            6
    2.21    Plan Year                                       6
    2.22    Tax-Qualified Limits                            7
    2.23    Trust                                           7
    2.24    Trustee                                         7

ARTICLE 3   PARTICIPATION AND BENEFITS                      7

    3.1     Participation                                   7
    3.2     Accounts                                        7
    3.3     Benefit at Termination of Employment            8
    3.4     Death Benefit                                   9
    3.5     Forfeiture of Benefit                           11
    3.6     Minors and Incompetents                         11
    3.7     Source of Payment of Benefits                   11

ARTICLE 4   THE TRUST                                       12

    4.1     Establishment of Trust                          12

ARTICLE 5 ADMINISTRATION

    5.1     Procedure                                       12
    5.2     Cooperation with Actuary                        12
    5.3     Duties                                          13
    5.4     Indemnification                                 14
    5.5     Mutual Exclusion of Responsibility              14
    5.6     Claims Procedure                                14
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ARTICLE 6   AMENDMENT AND TERMINATION                       16

    6.1     Amendment                                       16
    6.2     Termination                                     16

ARTICLE 7   MISCELLANEOUS                                   17

    7.1     Nonassignability of Benefits                    17
    7.2     Tax Withholding                                 17
    7.3     Rights of Participants and others               17
    7.4     Release by Participants, Etc                    18
    7.5     Construction                                    18
    7.6     Notices                                         18








































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                        IONICS, INCORPORATED

               SUPPLEMENTAL EXECUTIVE RETIREMENT PLAN

    Ionics, Incorporated, a Massachusetts corporation (the "Company"),
hereby adopts the Ionics, Incorporated Supplemental Executive
Retirement Plan as set forth below, effective as of January 1, 1996.

                              ARTICLE I

                               Purpose

    The purpose of the Plan is to provide specified retirement
benefits to the select group of officers and key employees
participating in the Plan, in addition to the benefits to which they
are entitled under the Pension Plan.  The Company intends that for
purposes of Title I of ERISA, the Plan constitute an unfunded
arrangement maintained for the purpose of providing deferred
compensation for a select group of management or highly compensated
employees.  If the Committee determines that any Participant, with
respect to any period, is not a member of such a select group for
purposes of ERISA, the Committee may, after notice to such person,
terminate such person's participation in the Plan, and cause such
person's Account to be paid to him as soon as practicable or to be
transferred to a trust for his sole benefit, which trust is not
subject to title I of ERISA.

                              ARTICLE 2

                             Definitions

      2.1   "Account" means a bookkeeping account maintained for a
Participant, to which amounts are credited and charged as described in
Section 3.2.

      2.2   "Actuary" means the enrolled actuary selected from time to
time by the Committee.

      2.3   "Additional Annuity Benefit" means the excess, as of the
end of a Plan Year, of (a) a Participant's projected annuity benefit
at his Normal Retirement Date, calculated under the normal retirement
benefit formula in the Pension Plan but taking into account his
Compensation without reference to the Tax Qualified Limits, over (b)
his projected annuity benefit at his Normal Retirement Date as
calculated for purposes of the Pension Plan; provided, however, that
if the Pension Plan is amended after the date hereof to "update" again
the Base Monthly Salary (as defined in the Pension Plan) which is
employed to calculate such annuity benefit, the Board may in its
discretion specify that such amendment is to be disregarded under this
clause (b), is to be modified as the Board may specify, or is to be
implemented in accordance with an effective date or a schedule
specified by the Board for purposes of this Plan.

    2.4     "Beneficiary" means the person(s) or entity(ies)
identified with respect to a Participant pursuant to Section 3.4.
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    2.5     "Benefit" means the amount that a Participant is entitled
to be paid under the Plan upon the termination of his employment.

    2.6     "Board" means the Board of Directors of the Company.

    2.7     "Cause" means any of the following: (a) the willful and
continued failure (other than by reason of incapacity due to physical
or mental illness) of a Participant to perform satisfactorily the
duties consistent with his title and position reasonably required of
him by the Board or supervising management after a written demand for
substantial performance is delivered to the Participant by the Board
or supervising management, which demand specifically identifies the
manner in which the Board or supervising management believes the
Participant has not satisfactorily performed his duties; (b) the
commission by a Participant of a felony, or the perpetration by a
Participant of a dishonest act or common law fraud against the
Company; (c) the use by a Participant of confidential information
available to him by reason of his employment, for any purpose other
than the sole interest of the Company or its client; or (d) any other
willful act or omission which is injurious to the financial condition
or business reputation of the Company; provided, however, that no act
or failure to act shall be deemed "willful" unless done, or omitted to
be done, not in good faith and without reasonable belief that the act
or omission was in the best interest of the Company.

  2.8       "Change of Control" means the purchase or other
acquisition by any person, entity or group of persons, within the
meaning of Section 13(d) or 14(d) of the Securities Exchange Act of
1934 (the "Act"), or any comparable successor provisions, of
beneficial ownership (within the meaning of Rule 13d-3 promulgated
under the Act) of 30 percent or more of either the outstanding shares
of common stock or the combined voting power of the Company's then
outstanding voting securities entitled to vote generally, or the
approval by the stockholders of the Company of a reorganization,
merger or consolidation, in each case, with respect to which persons
who were stockholders of the Company immediately prior to such
reorganization, merger or consolidation do not, immediately
thereafter, own more than 50 percent of the combined voting power
entitled to vote generally in the election of directors of the
reorganized, merged or consolidated company's then outstanding
securities, or a liquidation or dissolution of the Company or the sale
of all or substantially all of the Company's assets.

     2.9    "Code" means the Internal Revenue Code of 1986, as amended
from time to time.

      2.10  "Committee" means the Compensation Committee of the Board
or such other committee consisting of two or more individuals (who
may, but need not be, officers or directors of the Company) which is
appointed by the Board to administer this Plan.

      2.11  "Company" means Ionics, Incorporated and any successor to
all or a major portion of its property or business.

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      2.12  "Compensation" means the Compensation of a Participant
for a calendar year as defined in Article 2 of the Pension Plan.

      2.13  "Employment Termination" means a Participant's termination
of employment by the Company within 24 months following a Change of
Control or the Participant's Retirement (as defined in Section 2 of
the Pension Plan) provided, however, that a Participant's Employment
Termination will be deemed to have occurred in any event upon the
later to occur of his 65th birthday and his termination of employment
by the Company.

      2.14  "ERISA" means the Employee Retirement Income Security Act
of 1974, as amended.

      2.15  "Executive" means any officer or key employee of the
Company whose Compensation exceeds the limit in effect pursuant to
Section 401(a)(17) of the Code with respect to any Plan Year.

      2.16  "Interest Rate" means an annual rate of interest specified
for a Plan Year by the Committee, in consultation with the Actuary.

      2.17  "Participant" means an Executive who has commenced
participation in the Plan and whose Benefit has not been paid in full.

      2.18  "Pension Plan" means the Ionics, Incorporated Retirement
Plan as it may be amended from time to time.

      2.19  "Pension Plan Amount" means the excess of (a) the present
value required to be invested on the last day of the Plan Year in
order to produce a future value on a Participant's 65th birthday equal
to his Additional Annuity Benefit, assuming an interest rate equal to
the Interest Rate for the Plan Year for which the Pension Plan Amount
is being determined and otherwise using the actuarial assumptions
which are then employed for purposes of the Pension Plan, over (b) the
balance of the Participant's Account as of the end of the Plan Year
(disregarding the Pension Plan Amount for that Plan Year).

      2.20  "Plan" means the plan embodied in this instrument, as from
time to time amended.

2.21 "Plan Year" means the calendar year.

      2.22  "Tax-Qualified Limits" means the dollar amount in effect
from time to time pursuant to Section 401(a)(17) of the Code and the
limitations on benefits in effect from time to time under Section 415
of the Code.

      2.23  "Trust" means-the trust fund established pursuant to the
Plan.

      2.24  "Trustee" means the trustee named in the agreement
establishing the Trust and such successor and/or additional trustees
as may be named pursuant to the terms of the agreement establishing
the Trust.
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                              ARTICLE 3

                     Participation and Benefits

      3.1   Participation.  Each Executive employed by the Company on
the last day of the initial Plan Year (1996) shall become a
Participant in the Plan as of the effective date hereof, or as of the
first date of such later Plan Year in which he becomes an Executive.

      3.2   Accounts.  The Committee or its delegate shall maintain on
the books of the Company and in the Trust an Account for each
Participant, and shall credit to each Account as of the last day of
each Plan Year the Pension Plan Amount, as calculated by the Committee
or its delegate, in consultation with the Actuary.  The balance of the
Account shall be reduced by the amount of any Benefit paid to or in
respect of a Participant.  The Company will pay an amount to the Trust
with reasonable promptness after the Pension Plan Amount for any Plan
Year has been determined so that the Trust is caused to hold assets
equal in value to the sum of each Participant's Account.  The Company
shall direct the Trustee to invest the Account as the Company shall
determine.

      3.3   Benefit at Termination of Employment.  A Benefit shall be
payable to a Participant by reason of his Employment Termination in
the amount credited to the vested portion of his Account at the time
of payment.  A Participant's Account shall vest to the extent his
benefit under the Pension Plan is vested.  The balance of his Account
shall be credited with interest at the short-term "applicable federal
rate" under Section 1274(d) of the Code from the last day of the Plan
Year for which he last accrues Benefit Service under the Pension Plan
until such Account has been completely paid.  Subject to Sections 3.4
and 3.5, a Participant's Benefit shall be paid in one of the following
forms, according to the Participant's written election:

            (a) a single sum paid within 90 days after the end of the
Plan Year following the Participant's Employment Termination;

            (b) a series of two substantially equal annual
installments beginning within 90 days after the date of the
Participant's Employment Termination;

            (c) a series of five substantially equal annual
installments beginning within 90 days after the date of the
Participant's Employment Termination; or

            (d) a series of ten substantially equal annual
installments beginning within 90 days after the date of the
Participant's Employment Termination.  A Participant's election
pursuant to this Section 3.3 must be delivered to the Committee or its
delegate no later than 30 days after he becomes a Participant, and may
be changed only at such time and in such manner as the Committee may
permit.  If a Participant fails to deliver an election within that 30-
day period, his Benefit shall be paid in a single sum no later than 90
days after the end of the Plan Year following his Employment
Termination.
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    A series of installments shall be considered substantially equal
if the amount distributed in each Plan Year equals (a) the balance of
the Participant's Account as of the last day of the Plan Year most
recently ended before the date of payment, divided by (b) the number
of installments remaining to be paid.  Payments made after the initial
installment shall be-made an or about the anniversary date of the
initial installment.

     3.4    Death Benefit.  A death benefit shall be payable to the
Beneficiary of a Participant who dies while employed by the Company,
or who dies after his employment by the company has terminated but
before the Benefit to which he is entitled has been paid.  The amount
of the death benefit shall be equal to the balance of the deceased
Participant's Account as of the date of his death.  A Participant may
designate one or more persons or entities to receive death benefits
under the Plan by completing and delivering to the Committee or its
delegate during his lifetime a written designation in the form
prescribed by the Committee or its delegate.  A Participant may change
or revoke any such designation, without the knowledge or consent of
any party, by completing and delivering to the Committee or its
delegate another such form.  In every case, the form most recently
dated and delivered to the Committee or its delegate before the date
of a Participant's death shall cancel and supersede any such form
dated earlier.  Payment of any benefit due under the Plan with respect
to a Participant who fails to designate a Beneficiary, or whose
designated Beneficiary is no longer living at the Participant's death,
will be made to the Participant's surviving spouse; or if he is not
survived by his spouse, to his children by right of representation; or
if he is survived by neither spouse nor children, to his parents; or
if he is survived by none of the foregoing, to his estate.

     The death benefit shall be paid in a single sum as soon as
practicable after the Participant's death.  Payment with respect to a
Beneficiary who survives the Participant but dies before payment of
the Benefit under this Section 3.4 has been made will be made to the
Beneficiary's estate.

      3.5 Forfeiture of Benefit.  Notwithstanding any other provision
of the Plan, neither a Participant nor any  Beneficiary of a
Participant shall receive any Benefit under the Plan if the
Participant is dismissed from employment with the Company for Cause.

      3.6   Minors and Incompetents.  In the event that any Benefit
becomes payable to a minor or to a person under legal disability, or
to a person not judicially declared incompetent but whom the Committee
or its delegate considers unable properly to administer the Benefit by
reason of physical or mental disability, then the Benefit shall be
paid out in such of the following ways as the Committee or its
delegate deems best, and the Committee and the Company shall incur no
liability therefor: (a) directly to such person; (b) to the legally
appointed guardian or conservator of such person; or (c) to some
relative or friend for the care and support of such person.

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      3.7   Source of Payment of Benefits.  The Benefit provided under
the Plan with respect to a Participant shall be payable from the Trust
or from the general assets of the Company.  If the Trust does not have
sufficient assets to pay any amount owed under the Plan with respect
to a Participant, the Company shall make such Payment.  At no time
shall a Participant or Beneficiary have, by reason of the Plan, any
right, title, or interest superior to that of a general unsecured
creditor of the Company, in or to any asset or assets or of the
Company.

                                -12-

                              ARTICLE 4

                              The Trust

      4.1   Establishment of Trust.  The Company shall establish the
Trust with the Trustee, pursuant to such terms and conditions as are
set forth in the Trust agreement to be entered into between the
Company and the Trustee.  The Trust is intended to be treated as a
"grantor" trust under the Code, and the establishment of the Trust is
not intended to cause any Participant to realize current income on
amounts contributed thereto, and the Trust shall be so interpreted.

                              ARTICLE 5

                           Administration

      5.1   Procedure.  The Committee will be the administrator of the
Plan.  The Committee may take any decision or action in connection
with the Plan by a majority of its members.  Decisions in connection
with the Plan may be made and evidenced by a written document signed
by a majority of the Committee's members, without a formal meeting of
the Committee.  The Committee may delegate to one or more officers of
the Company any duty as to which the Plan specifically permits such
delegation, but no duty of the committee may be delegated to an
Executive who is or has been a Participant.

      5.2   Cooperation with Actuary. The Committee or its delegate
shall provide to the Actuary such information as to Participants'
compensation, accrued benefits under the Pension Plan, length of
service, age and other information that the Actuary may request in
connection with the calculation of the Pension Plan Amount.

     5.3    Duties.  In addition to the powers and duties specified
elsewhere in the Plan, the Committee shall:

            (a) determine all matters relating to the eligibility of
persons to become Participants in the Plan;

            (b) determine whether or not any employee of the Company
has become a Participant in the Plan;

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            (c) determine whether and when the employment of any
Participant has been terminated and, to the extent material to a
determination of a benefit hereunder, the cause of such termination;
and

            (d) decide all questions which may arise from time to time
with respect to the rights under the Plan of employees of the Company,
Participants, and any other persons who claim to be entitled to
benefits under the Plan.

     The Committee shall have exclusive discretionary authority to
construe and interpret the Plan document; provided, however, that in
exercising its powers and duties the Committee shall treat alike
Participants and Beneficiaries in like circumstances.

      5.4   Indemnification.  The Company agrees to indemnify and save
harmless each member of the Committee and any delegate of the
committee against any and all liability occasioned by or arising out
of any action with respect to the Plan taken, suffered or omitted in
good faith by him.

      5.5   Mutual Exclusion of Responsibility.  Neither the Trustee
nor the Company shall be obliged to inquire into or be responsible for
any act or failure to act, or the authority therefor, on the part of
the other.

      5.6   Claims Procedure.  A Participant or other person who
asserts a right to any benefit under the Plan which he has not
received must file a written claim with the Administrator.  If the
Administrator wholly or partially denies the claim, it shall within 90
days of receipt of the claim provide a written notice of denial to the
claimant, setting forth:

            (a) specific reasons for the denial of the claim,

            (b) specific reference to pertinent provisions of the Plan
on which the denial is based,

            (c) a description of any additional material or
information necessary to perfect the claim and an explanation of why
such material or information is necessary, and

            (d) an explanation of the Plan's claims review procedure.
    A claimant whose application for benefits is denied, or who has
received neither an affirmative reply nor a notice of denial within 90
days after filing his claim, may request a full and fair review of the
decision denying the claim.  The request must be made in writing to
the Administrator within 60 days after receipt of the notice of denial
(or, if no notice of denial is issued, within 60 days after the
expiration of 90 days from the filing of the claim).  In connection
with the review, the claimant or his authorized representative may:

      (a)   request a hearing by the Administrator upon written
application to the Administrator,
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      (b)   review pertinent documents in the possession of the
Administrator, and

      (c)   submit issues and comments in writing to the Administrator
to review.

      A decision on review by the Administrator shall be made
promptly, and not later than 60 days after the receipt by the
Administrator of a request for review, unless special circumstances
(such as a need to hold a hearing) require an extension of time for
processing, in which case the claimant will be so notified of the
extension and a decision shall be rendered as soon as possible, and
not later than 120 days after the receipt of the request for review.
The decision shall be in writing and shall include specific reasons
for the decision written in a manner calculated to be understood by
the claimant, and specific reference to the pertinent provisions of
the Plan on which-the decision is based.  The decision of the
Administrator shall be final and binding upon all parties.

                              ARTICLE 6

                      Amendment and Termination

     6.1    Amendment.  The Company shall have the right, at any time
and from time to time, to modify or amend the Plan by an instrument in
writing, executed by a duly authorized officer of the Company and
delivered to the Committee; provided, however, that no amendment shall
reduce the balance of a Participant's Account without his written
consent.

     6.2    Termination.  Although the Company expects to continue the
Plan indefinitely, it expressly reserves the right to terminate it in
whole or in part at any time by an instrument in writing delivered to
the Committee, effective on the date specified in such instrument.
Upon termination of the Plan, the Committee may in its discretion
permit each Participant who is then employed with the Company (or if
the Plan is partially terminated, each Participant affected by the
termination) to receive a Benefit equal to the balance of his Account
as of the date of such termination or partial termination, payable as
if the Participant had then terminated his employment.  To the extent
a Participant does not receive his Benefit upon termination of the
Plan, his Account shall continue to be maintained in accordance with
Section 3.2, and shall be payable in accordance with Section 3.3,
notwithstanding that thereafter there will be no Pension Plan Amount
added to the Account.

                              ARTICLE 7

                            Miscellaneous

      7.1   Nonassignability of Benefits.  No right or claim to any
benefit hereunder will be assignable by any Participant or
Beneficiary, nor subject to garnishment, attachment, execution or levy
of any kind.  Any attempt to assign, transfer, pledge, encumber,
commute or anticipate payment of benefits hereunder will be void.

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      7.2   Tax Withholding.  All payments under this Plan shall be
subject to such tax withholding as may be required by law.

      7.3   Rights of Participants and Others.  Except as expressly
set forth herein, nothing contained in the Plan shall be deemed to
give any Participant the right to be retained in the employ of the
Company, or to confer upon or create in any Participant or other
person any rights of any name or nature, legal or equitable.  Neither
anything contained herein nor any action taken by the Company
hereunder shall in any way prevent it from terminating the employment
of any Participant at any time, or subject it to any liability for
such termination, nor shall it be deemed to give the Company the right
to require the Participant to remain in its service or to interfere
with the Participant's right to terminate his service at any time.

      7.4   Release by Participants, Etc.  Except to the extent that
it relieves the Company or the Committee from responsibility or
liability for any responsibility, obligation or duty owing to the Plan
or to any Participant or Beneficiary, any payment made in accordance
with the provisions of the Plan to any person entitled to a Benefit
shall to the extent thereof be in full satisfaction of all claims
against the Company and the Committee, either of which may require as
a condition precedent to such payment that the recipient execute a
receipt and release therefor in such form as shall be determined by
the Company or the Committee, as the case may be.

      7.5   Construction.  The Plan shall be construed, and the rights
and liabilities of all persons hereunder shall be determined, in
accordance with the laws of the Commonwealth of Massachusetts, to the
extent that they are not preempted by ERISA.  Masculine pronouns shall
include both masculine and feminine genders, and singular words shall
include the plural, wherever the context permits.

      7.6   Notices.  Any notice under the Plan will be deemed to have
been properly delivered if it is in writing and is delivered in hand
or sent by registered mail, postage prepaid, to the party addressed as
follows, unless another address has been substituted by notice so
given:

     To a Participant: To his address as set forth in the payroll
records of the Company.

     To the Committee: Care of the Company, at its address as shown
directly below.

To the Company:        Ionics, Incorporated
                       65 Grove Street
                       Watertown, MA 02172
                       Attention: Stephen Korn, Esq.

     IN WITNESS WHEREOF, the Company has caused this document to be
executed this day of 1996.

                       Ionics, Incorporated

                       By:

Attest:

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