<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2017-03-17</periodOfReport>

    <issuer>
        <issuerCik>0001196298</issuerCik>
        <issuerName>NEPHROS INC</issuerName>
        <issuerTradingSymbol>NEPH</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001698052</rptOwnerCik>
            <rptOwnerName>Astor Andrew</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O NEPHROS, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>41 GRAND AVENUE</rptOwnerStreet2>
            <rptOwnerCity>RIVER EDGE</rptOwnerCity>
            <rptOwnerState>NJ</rptOwnerState>
            <rptOwnerZipCode>07661</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2017-03-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>166666</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>166666</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>.4599</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F2"/>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2027-02-13</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>289785</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>289785</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeTransaction>
            <securityTitle>
                <value>Warrants (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>.30</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2017-03-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>166666</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2017-03-17</value>
            </exerciseDate>
            <expirationDate>
                <value>2022-03-17</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>166666</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>166666</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The reported securities have a purchase price of $0.30 per share of Common Stock. In addition, the reporting person received a Warrant to purchase a number of shares of Common Stock equal to 100% of the number of shares of Common Stock otherwise purchased. The reporting person purchased 166,666 shares of Common Stock and was issued a related Warrant to acquire up to 166,666 shares of Common Stock.</footnote>
        <footnote id="F2">On 2/13/17, the Reporting Person was granted an option to purchase up to 579,571 shares of common stock of the Company. 12.5% of the shares subject to the option (relating to a total of 72,446 shares) vest on 2/13/18; 37.5% of the shares subject to the option (relating to a total of 217,339 shares) vest quarterly in 12 equal amounts, commencing on 5/13/18; 20% of the shares subject to the option (relating to a total of 115,914 shares) will vest, if ever, upon approval of listing of the Company's common stock on the NASDAQ Stock Market, New York Stock Exchange or such other national securities exchange approved by the Board; 10% of the shares subject to the option (relating to a total of 57,957 shares) will vest, if ever, on the February 1st following the Company's first completed fiscal year in which annual revenue exceeds $6,000,000; (continued)</footnote>
        <footnote id="F3">and 20% of the shares subject to the option  (relating to a total of 115,914 shares) will vest, if ever, on the February 1st following the Company's first completed fiscal year in which annual revenue exceeds $10,000,000.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Amanda Lorentz as attorney-in-fact for Andrew Astor pursuant to power of attorney previously filed.</signatureName>
        <signatureDate>2017-03-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
