Alkali metals are known to react vigorously with water, producing hydrogen gas and a hydroxide solution. Therefore, all alkali metals will react with water in the same manner, regardless of their position in the periodic table.

Alkali metals all have one electron in their outer shell, so they can give it up easily and produce hydrogen gas and a hydroxide. However, the ease of losing that electron changes with size: as you go down the group, the outer electron is farther from the nucleus and more shielded, making it easier to lose. Lithium at the top reacts slowly, almost like a mild soap, while sodium and potassium react rapidly and violently, and francium (if it could be tested) would react even more explosively. Thus the position in the periodic table determines how vigorously each metal reacts with water, not just the fact that they are alkali metals. A simple example: sodium metal, when dropped into water, splashes and fizzles loudly, whereas lithium metal barely fizzles and produces only a small amount of hydrogen.