"De-ionized Water"

City water and well water will have some level of contaminants which can possibly upset the balance in the plating tank, or leave salt stains on the finished work.

Depending on how good or bad the city water is, it may or may not be okay to use it for making up the plating baths and other process solutions, and for rinsing between the process steps and for final rinsing. If the water quality is problematic, an ion exchange process can be employed. For most plating and rinsing needs, running the water thru a cation-exchange column followed by an anion-exchange column will be sufficient to remove the great majority of contaminants. For semi-conductor work however, where super-purity is required, water is usually subsequently run through a mixed-bed column, where the water encounters a particle of cation exchange resin, then a particle of anion exchange resin, then another cation, another anion, etc., thousands of times -- equivalent to sequentially passing it through thousands of ion exchange columns in series. Rinse tanks usually require continuously running water, so continuously feeding them with de-ionized water can be expensive and impractical. When de-ionized water is required for a rinse tank, the usual approach is to continuously recirculate the water in the rinse tank through the de-ionization columns rather than using continuously overflowing water in the rinse tank.