ABSTRACT: According to Thales of Miletus, water is the arché or primary principle from which all things originate and to which all things ultimately return. We begin this chapter by analyzing this teaching in light of the state of philosophy and science during Thales’ time. We continue by focusing on the possible relations between water as the arché and wisdom. After establishing that, strictly speaking, there can be no ethics of water as such, but only an ethics of human action involving water, we shall put forward some proposals that connect water and ethics under the influence of Thales’ discussion. The ethics of water use and water technology should be analyzed within the context of human beings manifold relation with nature. A balance has to be struck between an attitude of contemplation (theoria) or respect (epimeleia) and one of dominion and control as is proper of technology (techne); and within the latter, between the perspective of water as an element in life-sustaining biological exchanges and the perspective of water storage, treatment and distribution that makes the biological exchanges involving water possible. In the end, suggestions on how human excellences of virtues come into play in each of these actions are offered.