In fragment 5 on pg 15 of A Presocratics Reader, Aristotle discusses the principles in which he and other early philosophers, including Thales, believed. They declare first off that the only principles that serve to be principles of everything, of the principles of matter, and this is because everything is made up of matter. He goes on to describe how the main principle of matter is described by Thales to be water, his reasoning being that “the nourishment of all things is moist.”
By this idea, he means that water is within or related to most objects of matter. He sees plants and animals needing water to survive, everything alive is moist, and even hot itself comes from water. Thales even takes it further to declare that the earth rests on water, meaning that he believed water was such a principle of matter that the earth was floating on water itself, rather than floating in open air/space.
To a certain extent, I found it interesting that early philosophers took such an interest to water. Water really is crucial to all living things, and is even involved in the formation of bonds between elements of abiotic structures. Even though the Earth doesn’t actually float in a pool of water, I still found it intriguing that he realized the importance of water in our universe, even without knowing to true depth of which we do now.