A metal hydroxide and hydrogen gas form when a metal reacts with water. The metal hydroxide is a strong base. Reactions between a metal (especially an alkali metal) and water usually produce a violent scene.
According to a page on the Towson University website, when a metal reacts with water, the metal combines with oxygen and hydrogen to form a strong base. The oxygen and hydrogen are combined chemically to form a hydroxide, which acts as a single entity. The metal has few valence electrons, so it tends to act as an electron donor; the hydroxide is an electron acceptor. The alkali metals such as sodium, potassium and cesium are so reactive that their reactions with water may cause explosions.