Not for drinking, but for cleaning and rinsing the sample handling tools and containers. Since the early 1970s sample tools and containers were cleaned first with mild surfactant solution in an ultrasonic device. Sometimes an acid rinse was used to remove traces of lead from the manufacturing process. But all tools were finally rinsed with distilled Freon and dried. As a fluorocarbon, Freon was ideal because it did not leave a hydrocarbon residue. Freon was a good solvent for non-polar contaminants, it was non-flammable for added safety, and it dried rapidly removing moisture from the items. Alas, Freon's side-effect of destroying ozone in the upper atmosphere, led the curator to replace Freon cleaning with with Ultra Pure Water (UPW) in 1994.

Technical development of UPW cleaning was led by the semiconductor industry. Very pure water is an excellent solvent. Purity of the water is continually measured by the resistivity of the water. Curatorial UPW exceeds 18 MW-cm. Other measures of cleanliness performed on batch samples include inorganic ions (1 ppb level), total organic carbon (100 ppb level), and culturing/endotoxin tests for microorganisms (none confirmed). The team is in the process of upgrading the batch testing procedures.

How is ultra pure water created? Starting with water purified by reverse osmosis, water is passed through 5 µm filters, cation/anion absorbers and then into a continually circulating closed loop. In this loop are filters to remove particles < 0.2 µm, an ultraviolet source to kill microorganisms, and organic carbon absorbers. The important concept is to keep the water continually moving with no "dead" space for non-circulating water, for that is where microbes can grow. Because pure water is such an agressive solvent, the plumbing for the entire system is made of polyvinylidene fluoride (PVDF), a non-leaching material.

Finally, some UPW is drawn off the loop and heated to 160° F just before the water is used to intensively rinse the tools. The tools are then transferred to an oven with highly-filtered air circulation for drying.

Ultra pure water is just one technology used in the curatorial cleaning process.