-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 EbTnV9SivkIdIclvbmLQgWgteBiRG3T3BeTzZBYi5JUx7PAZFYEEYMowbKiaf5Yp
 AaKehYJ04sZnG+K5QBYsPQ==

<SEC-DOCUMENT>0000052466-03-000026.txt : 20030509
<SEC-HEADER>0000052466-03-000026.hdr.sgml : 20030509
<ACCEPTANCE-DATETIME>20030509093046
ACCESSION NUMBER:		0000052466-03-000026
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20030507
FILED AS OF DATE:		20030509

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			IONICS INC
		CENTRAL INDEX KEY:			0000052466
		STANDARD INDUSTRIAL CLASSIFICATION:	SPECIAL INDUSTRY MACHINERY, NEC [3559]
		IRS NUMBER:				042068530
		STATE OF INCORPORATION:			MA
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		65 GROVE ST
		CITY:			WATERTOWN
		STATE:			MA
		ZIP:			02172
		BUSINESS PHONE:		6179262500

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			WANG DANIEL I C
		CENTRAL INDEX KEY:			0001162750

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07211
		FILM NUMBER:		03689116

	BUSINESS ADDRESS:	
		STREET 1:		C/O MASSACHUSETTS INSTITUTE
		STREET 2:		77 MASSACHUSETTS AVE.
		CITY:			CAMBRIDGE
		STATE:			MA
		ZIP:			02139-4307
		BUSINESS PHONE:		6172532126
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>primary_doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>

<ownershipDocument>

    <documentType>4</documentType>

    <periodOfReport>2003-05-07</periodOfReport>


    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000052466</issuerCik>
        <issuerName>IONICS INC</issuerName>
        <issuerTradingSymbol>ION</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001162750</rptOwnerCik>
            <rptOwnerName>WANG DANIEL I C</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeSecurity>
        <securityTitle>
            <value>Common Stock</value>
        </securityTitle>
        <transactionDate>
            <value>2003-05-07</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>A</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>397</value>
                <footnoteId id="F1"/>
            </transactionShares>
            <transactionValue>
                <value>18.9</value>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>2927</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </nonDerivativeSecurity>

    <derivativeSecurity>
        <securityTitle>
            <value>Stock Option (right to buy)</value>
        </securityTitle>
        <conversionOrExercisePrice>
            <value>18.9</value>
        </conversionOrExercisePrice>
        <transactionDate>
            <value>2003-05-07</value>
        </transactionDate>
        <transactionCoding>
            <transactionFormType>4</transactionFormType>
            <transactionCode>A</transactionCode>
            <equitySwapInvolved>0</equitySwapInvolved>
        </transactionCoding>
        <transactionTimeliness>
            <value></value>
        </transactionTimeliness>
        <transactionAmounts>
            <transactionShares>
                <value>4000</value>
                <footnoteId id="F2"/>
            </transactionShares>
            <transactionValue>
                <value>0</value>
                <footnoteId id="F2"/>
            </transactionValue>
            <transactionAcquiredDisposedCode>
                <value>A</value>
            </transactionAcquiredDisposedCode>
        </transactionAmounts>
        <exerciseDate>
            <value>2003-11-07</value>
        </exerciseDate>
        <expirationDate>
            <value>2013-05-07</value>
            <footnoteId id="F3"/>
        </expirationDate>
        <underlyingSecurity>
            <underlyingSecurityTitle>
                <value>Common Stock</value>
            </underlyingSecurityTitle>
            <underlyingSecurityShares>
                <value>4000</value>
            </underlyingSecurityShares>
        </underlyingSecurity>
        <postTransactionAmounts>
            <sharesOwnedFollowingTransaction>
                <value>4000</value>
            </sharesOwnedFollowingTransaction>
        </postTransactionAmounts>
        <ownershipNature>
            <directOrIndirectOwnership>
                <value>D</value>
            </directOrIndirectOwnership>
        </ownershipNature>
    </derivativeSecurity>

    <footnotes>
        <footnote id="F1">Represents shares acquired by reporting person as payment of retainer fee pursuant to Ionics, Incorporated 1998 Non-Employee Directors Fee Plan in a transaction exempt under Rule 16b-3.</footnote>
        <footnote id="F2">Grant to reporting person of option to buy 4,000 shares of Common Stock under the Ionics, Incorporated 2003 Non-Employee Directors Stock Option Plan in a transaction exempt under Rule 16b-3.</footnote>
        <footnote id="F3">Will expire earlier in the event the reporting person ceases to be a director.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Daniel I. C. Wang</signatureName>
        <signatureDate>2003-05-07</signatureDate>
    </ownerSignature>

</ownershipDocument>

</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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