Table of Contents

Exhibit31.1

CERTIFICATION PURSUANT TO SECTION 302 OF THESARBANES-OXLEY ACT OF 2002

I, William H. Joyce, certifythat:

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| 1.  | I have reviewed this quarterly report onForm 10-Q of Nalco Holding Company; |

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| 2.  | Based on myknowledge, this report does not contain any untrue statement ofmaterial fact or omit to state a material fact necessary to make thestatements made, in light of the circumstance under which suchstatements were made, not misleading with respect to the period coveredby this report; |

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| 3.  | Based on my knowledge, thefinancial statements, and other financial information included in thisreport, fairly represent in all material respects the financialcondition, results of operations and cash flows of the registrant, asof, and for, the periods presented in thisreport; |

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| 4.  | The registrant’s other certifyingofficer and I are responsible for establishing and maintainingdisclosure controls and procedures (as defined in Exchange Act Rules13a-15(e) and 15d-15(e)) and internal control over financial reporting(as defined in Exchange Act Rules 13a-15(f) and 15d-15(f)) for theregistrant and have: |

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|  | (a)  | Designed such disclosurecontrols and procedures, or caused such disclosure controls andprocedures to be designed under our supervision, to ensure thatmaterial information relating to the registrant, including itsconsolidated subsidiaries, is made known to us by others within thoseentities, particularly during the period in which this report is beingprepared; |

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|  | (b)  | Designed such internal control overfinancial reporting, or caused such internal control over financialreporting to be designed under our supervision, to provide reasonableassurance regarding the reliability of financial reporting and thepreparation of financial statements for external purposes in accordancewith generally accepted accountingprinciples; |

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|  | (c)  | Evaluated the effectiveness ofthe registrant’s disclosure controls and procedures andpresented in this report our conclusions about the effectiveness of thedisclosure controls and procedures, as of the end of the period coveredby this report based on such evaluation;and |

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|  | (d)  | Disclosed in this report any change inthe registrant’s internal control over financial reporting thatoccurred during the registrant’s most recent fiscal quarter thathas materially affected, or is reasonably likely to materially affect,the registrant’s internal control over financial reporting;and |

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| 5.  | The registrant’s other certifyingofficer and I have disclosed, based on our most recent evaluation ofinternal control over financial reporting, to the registrant’sauditors and the audit committee of the registrant’s board ofdirectors (or persons performing the equivalentfunctions): |

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|  | (a)  | All significant deficiencies andmaterial weaknesses in the design or operation of internal control overfinancial reporting which are reasonably likely to adversely affect theregistrant’s ability to record, process, summarize and reportfinancial information; and |

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|  | (b)  | Any fraud, whetheror not material, that involves management or other employees who have asignificant role in the registrant’s internal control overfinancial reporting. |

Date: August  9,2006

/s/ WILLIAM H.JOYCE

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Name:     WilliamH. Joyce

Title:       Chairmanand Chief Executive Officer

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