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                                                                     EXHIBIT 5.1


                       [Letterhead of Baker Botts L.L.P.]

February 5, 2001



Waste Management, Inc.
1001 Fannin Street, Suite 4000
Houston, Texas  77002

Ladies and Gentlemen:

                  We have acted as counsel for Waste Management, Inc., a
Delaware corporation (the "Company"), in connection with the preparation of the
prospectus supplement dated February 2, 2001 (the "Prospectus Supplement") with
respect to the Registration Statement on Form S-3 filed by the Company with the
Securities and Exchange Commission (the "Commission") under the Securities Act
of 1933, as amended (the "Securities Act"), relating to the issuance and sale of
$600,000,000 aggregate principal amount of the Company's 7 3/8% Senior Notes Due
2010 (the "Notes"), to be issued under an Indenture, dated as of September 10,
1997 (the "Indenture"), between the Company, formerly known as USA Waste
Services, Inc., and The Chase Manhattan Bank, as successor to Texas Commerce
Bank National Association, as trustee (the "Trustee").

                  In our capacity as your counsel in the connection referred to
above, we have examined the Restated Certificate of Incorporation and Bylaws of
the Company, each as amended to date, and have examined the originals, or copies
certified or otherwise identified, of the Indenture and corporate records of the
Company, including minute books of the Company as furnished to us by the
Company, certificates of public officials and of representatives of the Company,
statutes and other instruments and documents, as a basis for the opinions
hereinafter expressed. In giving such opinions, we have relied upon certificates
of officers of the Company with respect to the accuracy of the material factual
matters contained in such certificates. In making our examination, we have
assumed that all signatures on documents examined by us are genuine, that all
documents submitted to us as originals are authentic and that all documents
submitted to us as certified or photostatic copies conform with the original
copies of such documents.

                  On the basis of the foregoing, and subject to the assumptions,
limitations and qualifications set forth herein, we are of the opinion that the
Notes, when duly executed, authenticated, issued and delivered in accordance
with the provisions of the Indenture and the provisions of the Underwriting
Agreement and upon payment of the consideration therefor provided for therein,
will constitute legal, valid and binding obligations of


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Waste Management, Inc.                -2-                       February 5, 2001


the Company, enforceable against the Company in accordance with their terms,
except as the enforceability thereof is subject to the effect of (x) bankruptcy,
insolvency, reorganization, moratorium, fraudulent transfer or other laws
relating to or affecting creditors' rights generally and (y) general principles
of equity (regardless of whether such enforceability is considered in a
proceeding in equity or at law).

                  The opinions set forth above are limited in all respects to
matters of the Delaware General Corporation Law and the contract law of the
State of New York as in effect on the date hereof. At your request, this opinion
is being furnished to you for filing as Exhibit 5 to a Form 8-K to be filed with
the Commission. Additionally, we hereby consent to the reference to our Firm
under the caption "Legal Matters" in the Prospectus Supplement. In giving such
consent, we do not thereby concede that we are within the category of persons
whose consent is required under Section 7 of the Securities Act or the rules and
regulations of the Commission promulgated thereunder.

                                       Very truly yours,



                                       Baker Botts L.L.P.



JDK/ERH




