The ritual baths were fed by water from the aqueduct. Mikva'ot similar to those at Qumran were typical of public and private buildings in Jerusalem and elsewhere in the Second Temple period.
Qumran Mikva
This is one of several mikva'ot (ritual baths) found at the site. They were water-proofed with hydraulic plaster. The Mishnah notes the importance of immersion in water for spiritual purification and lists the requirements for such ritual baths.