In Judaism water is a symbol of life. It is no wonder that Sages tell us that when beginning a Jewish community our first act is to build a mikvah. Even before a synagogue is built we must have mayim chayim, “living waters” to be able to function as a Jewish community.
So critical and central to Jewish life is this mitzvah, that the Jews who were trapped on top of Masada nearly 2000 years ago, fighting the Roman army that surrounded them, constructed not one but two mikvaot. Even in the midst of those most difficult circumstances, this Jewish community could not function without a mikvah.