EXHIBIT 21
                              IONICS, INCORPORATED

                         SUBSIDIARIES OF THE REGISTRANT

                                                  State or Other Jurisdiction
      Name                                             of Incorporation
      ----                                        ---------------------------

Aqua Design, Inc.*                                       California
Elite Chemicals Pty. Ltd.                                 Australia
Favourable Trading Ltd. (dba Ionics Ireland)               Ireland
Fidelity Purewater, Inc.                                 California
Fidelity Water Systems, Inc.                             California
Global Water Services, S.A.+                               Panama
Ionics Acapulco, S.A.                                      Mexico
Ionics Agar Environmental Ltd.                             Israel
Ionics Asia-Pacific Pte. Ltd.                             Singapore
Ionics (Bermuda) Ltd.*                                     Bermuda
Ionics Caribbean Investors Ltd.                           St. Lucia
Ionics Constructors Trinidad Ltd.                    Trinidad and Tobago
Ionics Enersave Engineering Sdn Bhd**                     Malaysia
Ionics Foreign Sales Corporation Limited                   Jamaica
Ionics France S.A.                                         France
Ionics Freshwater Ltd.++                                  Barbados
Ionics Iberica, S.A.                                        Spain
Ionics Italba, S.p.A.+++                                    Italy
Ionics Korea                                              Delaware
Ionics Life Sciences, Inc.                               New Jersey
Ionics Mega a.s.***                                    Czech Republic
Ionics Nederland B.V.                                  The Netherlands
Ionics Taiwan, Inc.                                        Taiwan
Ionics Ultrapure Water Corporation                       California
Ionics (U.K.) Limited++++                              United Kingdom
Ionics Ventures Ltd.                                   United Kingdom
Ionics Water Resources Ltd.                                Israel
Ionics Watertec Pty. Ltd.                                 Australia
Resources Conservation Co. International                  Delaware
Separation Technology, Inc.****                           Minnesota
Sievers Instruments, Inc.                                 Colorado

*    The  Registrant,  either  directly,  through Aqua  Design,  Inc. or through
     Ionics (Bermuda) Ltd., wholly owns 13 corporations  incorporated in various
     Caribbean jurisdictions.  These subsidiary corporations own and operate, or
     operate and maintain,  desalination  plants for the supply of potable water
     to  resorts,  hotels  and  municipalities.

**   Registrant  through  Ionics  Iberica,  S.A.  owns 55% of this entity.  This
     entity has  subsidiary  operations in Malaysia and China.  Registrant is in
     the process of disposing of its  interest in this  entity.

***  Registrant owns 80% of this entity.

**** Owns a U.K.  subsidiary,  SeparaTech Limited.

+    This entity is wholly owned by Ionics (U.K.) Ltd.

++   Registrant owns 50% of this entity.

+++  This entity owns a 75% interest in Agrinord S.r.l., an Italian  corporation
     in the waste treatment business.

++++ This entity is wholly owned by Ionics Ventures Ltd.