Planet Earth makes its own water from scratch deep in the mantle

There is russian book called "Unknown Hidrogen"[1] and reflection on it in [2]. In short Earth core is much like iron + hidrogen. Hidrogen lefts core and travels to crust. Hidrogen bounds with oxygen and gives water.

I thing Google Translate will translate article well enough.

[1]https://www.ozon.ru/context/detail/id/3277980/ [2]http://lah.ru/text/sklyarov/earth-text.htm