Exhibit 3.13


                          CERTIFICATE OF INCORPORATION

                                       OF

                          HYDRO GATE ACQUISITION CORP.

     1. The name of the corporation is HYDRO GATE ACQUISITION CORP.

     2. The address of its registered office in the State of Delaware is
Corporation Trust Center, 1209 Orange Street, Wilmington, Delaware 19801. The
name of its registered agent at such address is The Corporation Trust Company.

     3. The nature of the business or purposes to be conducted or promoted is
to engage in any lawful act or activity for which corporations may be organized
under the General Corporation Law of Delaware.

     4. The total number of shares of stock which the corporation shall have
authority to issue is One Thousand (1,000) and the par value of each of such
share is One Cent ($.01).

     5. The name and mailing address of the Incorporator are Anthony T. Barnes,
600 Peachtree Street N.E., Suite 5200, Atlanta, Georgia 30308.

     6. The corporation is to have perpetual existence.

     7. In furtherance and not in limitation of the powers conferred by
statute, the board of directors is expressly authorized to make, alter or
repeal the bylaws of the corporation.

     8. Elections of directors need not be by written ballot unless the bylaws
of the corporation shall so provide.

     9. Meetings of stockholders may be held within or without the State of
Delaware, as the bylaws may provide. The books of the corporation may be kept
(subject to any provision





contained in the statutes) outside the State of Delaware at such place or
places as may be designated from time to time by the board of directors or in
the bylaws of the corporation.

     10. The corporation reserves the right to amend, alter, change or repeal
any provision contained in this certificate of incorporation, in the manner now
or hereafter prescribed by statute, and all rights conferred upon stockholders
herein are granted subject to this reservation.

     11. The corporation shall, to the fullest extent permitted by the
provisions of the General Corporation Law of the State of Delaware, as the same
may be amended or supplemented from time to time, indemnify any and all persons
whom it shall have the power to indemnify under Section 145 of the Delaware
General Corporation Law, as the same may be amended or supplemented from time
to time, to the fullest extent permitted by such Section 145 and the
Corporation's obligation to indemnify such persons hereunder shall: i) inure to
the benefit of the heirs, executors and administrators of such persons; and ii)
shall continue as to persons who have ceased to be directors, officers,
employees or agents of the Corporation.

     I, THE UNDERSIGNED, being the Incorporator hereinbefore named, for the
purpose of forming a corporation pursuant to the General Corporation Law of the
State of Delaware, do make this certificate, hereby declaring and certifying
that this is my act and deed and the facts herein stated are true, and
accordingly have hereunto set my hand this 3rd day of December, 2001.

                                              /s/ Anthony T. Barnes
                                              ---------------------
                                              Anthony T. Barnes, Incorporator