It says so in the 1955 wt.
*** w55 7/1 p. 402 par. 5 Were You Baptized? How? Why? ***
5 Commenting further on the matter of water baptism, The Catholic Encyclopedia states: “How natural and expressive the symbolism of exterior washing to indicate interior purification was recognized to be, is plain from the practice also of the heathen systems of religion. The use of lustral water is found among the Babylonians, Assyrians, Egyptians, Greeks, Romans, Hindus and other.” It is a fact that among the heathen, pagan religions washing and baptizing in water is also viewed as a sacrament that imparts much merit. Non-Catholic authorities agree with this Catholic authority that such is the case and thus two authorities unite in proving the non-Christian claim or theory that water baptism is a sacrament to be of demon or Devil origin.
They also say that baptism doesn't make you a member:
*** w55 7/1 p. 402 par. 4 Were You Baptized? How? Why? ***
For the same reasons immersion in water does not constitute an individual a member of the church or body of Christ, the congregation.
They then go on about how christian baptism is different. Problem w that is that the vast majority of jws don't have jesus as mediator to god, therefore their baptisms are not christian actions, but secular as a sign of joining the wt corporation. It's an interesting and contradictory wt article.
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