Exhibit 5.1

                               GOODWIN PROCTER LLP
                                 Exchange Place
                                Boston, MA 02109

                                   May 4, 2005

Watts Water Technologies, Inc.
815 Chestnut Street
North Andover, MA 01845

     Re:    Legality of Securities to be Registered
            under Registration Statement on Form S-3
            ----------------------------------------

Ladies and Gentlemen:

     This opinion is delivered in our capacity as counsel to Watts Water
Technologies, Inc., a Delaware corporation (the "Company"), in connection with a
registration statement on Form S-3 (the "Registration Statement") filed with the
Securities and Exchange Commission under the Securities Act of 1933, as amended
(the "Securities Act"), which relates to the sale from time to time of an
indeterminate amount of (i) debt securities ("Debt Securities"), and (ii) shares
of preferred stock, par value $.10 per share ("Preferred Stock"), shares of
Class A common stock, par value $.10 per share ("Class A Common Stock"),
depositary shares representing interests in Preferred Stock ("Depositary
Shares"), warrants to purchase Preferred Stock or Class A Common Stock
("Warrants"), stock purchase contracts and/or stock purchase units
(collectively, "Purchase Units"), or any combination of Preferred Stock, Class A
Common Stock, Depositary Shares, Warrants or Purchase Units (collectively, the
"Equity Securities") or Debt Securities (the Equity Securities and the Debt
Securities, collectively, the "Securities") of the Company having a maximum
aggregate public offering price of $300,000,000. The Registration Statement
provides that the Securities may be offered separately or together, in separate
series, in amounts, at prices, and on terms to be set forth in one or more
prospectus supplements (each a "Prospectus Supplement") to the prospectus
contained in the Registration Statement.

     In connection with this opinion, we have examined the restated certificate
of incorporation of the Company, as amended to the date hereof and on file with
the Delaware Secretary of State, the amended and restated by-laws of the
Company, as amended to the date hereof, and such records of corporate
proceedings of the Company as we have deemed appropriate for the purposes of
this opinion, the Registration Statement and the exhibits thereto.

     In rendering the opinions expressed below, we have assumed and have not
verified the genuineness of all signatures, the authenticity of all documents
submitted to us as originals, the conformity to original documents of all
documents submitted to us as certified or photostatic copies, the authenticity
of the originals of such latter documents, and the legal capacity of each
individual executing any document.

     We express no opinion concerning the laws of any jurisdictions other than
the laws of the United States of America, The Commonwealth of Massachusetts, the
State of New York, and the Delaware General Corporation Law.



Watts Water Technologies, Inc.
May 4, 2005
Page 2

     Based upon the foregoing, we are of the opinion that:

         (1)   (i) when the Debt Securities are specifically authorized for
issuance by the Company's Board of Directors or an authorized committee thereof
(the "Debt Securities Authorizing Resolution"), (ii) upon receipt by the Company
of the full consideration therefor as provided in the Debt Securities
Authorizing Resolution, and (iii) upon execution and authentication of the Debt
Securities as provided in the relevant indentures and the issuance of the Debt
Securities as described in the Registration Statement and a Prospectus
Supplement that is consistent with the Debt Securities Authorizing Resolution,
the Debt Securities will be binding obligations of the Company, enforceable in
accordance with their terms, except that (A) enforcement or the rights and
remedies created thereby may be limited by bankruptcy, insolvency, fraudulent
conveyance, reorganization, moratorium and similar laws of general applicability
relating to or affecting creditors' rights and by equitable principles which may
limit the right to obtain the remedy of specific performance or other injunctive
relief and (B) we express no opinion as to the legality, validity or binding
nature of a choice of law provision; and

         (2)   (i) when the Equity Securities are specifically authorized for
issuance by the Company's Board of Directors or an authorized committee thereof
(the "Equity Securities Authorizing Resolution"), (ii) upon receipt by the
Company of the full consideration therefor as provided in the Equity Securities
Authorizing Resolution, and (iii) upon the issuance of the Equity Securities as
described in the Registration Statement and a Prospectus Supplement that is
consistent with the Equity Securities Authorizing Resolution, the Equity
Securities will be legally issued, fully paid and nonassessable and the Warrants
and Purchase Units will be binding obligations of the Company.

     The foregoing assumes that all requisite steps will be taken to comply with
the requirements of the Securities Act and applicable requirements of state laws
regulating the offer and sale of securities.

     We hereby consent to being named as counsel to the Company in the
Registration Statement, to the references therein to our firm under the caption
"Legal Matters" and to the inclusion of this opinion as an exhibit to the
Registration Statement.

                                                   Very truly yours,

                                                   /s/ GOODWIN PROCTER LLP

                                                   GOODWIN PROCTER LLP