Pure water equipment improves the pretreatment system. For each membrane unit, we hope it can maximize its performance, achieve high desalination rates, high water permeability, and as long a service life as possible. To achieve these three goals, the quality of the feed water is crucial. Therefore, the raw water entering the reverse osmosis membrane unit must undergo proper pretreatment. Reasonable pretreatment is essential for the long-term safe operation of the reverse osmosis system. With pretreatment that meets the water quality requirements for reverse osmosis feed water, it ensures stable product water flow, maintains desalination rates at a certain level for an extended period, keeps the product water recovery rate unchanged for a long time, minimizes operating costs, and extends membrane life. Specifically, reverse osmosis pretreatment aims to: (1) Prevent membrane surface contamination, i.e., prevent suspended impurities, microorganisms, and colloidal substances from adhering to the membrane surface or clogging the water flow channels of the membrane elements. (2) Prevent scaling on the membrane surface. During the operation of the reverse osmosis system, due to water concentration, some insoluble salts may deposit on the membrane surface, so it is necessary to prevent the formation of these insoluble salts. (3) Ensure the membrane is protected from mechanical and chemical damage to maintain good performance and a sufficiently long service life. When selecting materials for reverse osmosis equipment pipelines, both internal and external factors must be considered. Internally, it involves the corrosion of the pipelines by water quality, while externally, it pertains to the operating environment.

Demineralized water refers to water from which salts have been removed or reduced to a certain extent. Its conductivity is generally 1.0–10.0 μS/cm, with a salt content of 1.5 mg/L.

If tap water is used, calcium and magnesium ions, impurities, and inorganic ions in the water will gradually be introduced into the electroplating tank and accumulate in the electroplating solution. When accumulated to a certain level, they will severely affect the appearance quality and internal corrosion resistance of the electroplating layer, easily leading to unqualified products and reducing the pass rate. Only pure water can thoroughly clean electroplated products. In the industry, the water quality requirements for cleaning small electroplated parts are even higher because workpieces after roughening have numerous micropores on their surfaces. The water rinse before the sensitization process must use pure water, and the rinse water must also include certain filtration facilities to prevent particles in the rinse water from forming "autocatalytic centers" in the electroless nickel solution, rapidly deteriorating the electroless nickel plating bath or affecting electroplating quality. For some decorative and high-appearance surface treatment industries, water quality requirements are also very high. In particular, the rinse after electroplating must use ultrapure water treated by a mixed-bed ion exchanger as the cleaning water, with conductivity below 1 μS/cm2, to thoroughly remove residual electroplating solution and other impurities from the workpiece. The process flow of ultrapure water equipment for the electroplating industry is: tap water raw water → raw water booster pump → sand filter → carbon filter → softener (selected based on regional differences) → safety filter → RO high-pressure pump → RO reverse osmosis system → RO water tank → pure water booster pump → mixed-bed ion exchange resin → terminal precision filter → equipment water (ultrapure water quality can reach 16 MΩ·cm). Certain heavy metals, such as chromium, can catalyze the oxidation of chlorine, leading to irreversible performance degradation of the membrane and causing membrane damage.