  We describe the design, installation, and operation of a purification system
that is able to provide large volumes of high purity ASTM (D1193-91) Type-I
water to a high energy physics experiment. The water environment is underground
in a lightly sealed system, and this provides significant challenges to
maintaining high purity in the storage pools, each of which contains several
thousand cubic meters. High purity is dictated by the need for large optical
absorption length, which is critical for the operation of the experiment. The
system is largely successful, and the water clarity criteria are met. We also
include a discussion of lessons learned.
