I’ve done research about scientists’ references to water.

In 1893, Nikola Tesla presented On Light and Other High Frequence Phenomena: 

For our existence and comfort we require heat, light and mechanical power. How do we now get all these?  We get them from fuel, we get them by consuming material. What will man do when the forests disappear, when the coal fields are exhausted?

Only one thing according to our present knowledge will remain; that is, to transmit power at great distances. Men will go to the waterfalls, to the tides, which are the stores of an infinitesimal part of Nature’s immeasurable energy.

Emphasis mine.

(As a side note: Tesla mentions about forests disappearing. The current view is that forests are - with proper care - renewable.)

In his other article, Our Future Motive Power, he goes deeper in analyzing different ways of harnessing power from nature’s resources, namely water.