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A new potable and cooling water supply at a hospital experienced corrosion (rust) in the drinking water distribution system. Despite efforts to prevent corrosion by adding a zinc phosphate [Zn^sub 3^(PO^sub 4^)^sub 2^] corrosion inhibitor, some corrosion persisted because of the aggressive water supply and low flow in portions of the system. An epoxy coating was applied on the waterside surfaces of the steel piping. The epoxy coating formed a protective barrier to prevent the water from contacting the steel surface.
A water distribution pipe system, made of unlined, welded, black steel pipes, was installed during the construction of a hospital in 1996. Rust-colored stains were soon observed on white fixtures, sinks, and porcelain after fixture installation. The entire system was flushed in April 1997 and samples of the incoming municipal water were analyzed. The tests indicated an increase in the water's iron content. After flushing, some areas of the pipe network were filled and remained stagnant until September 1997. The water source was switched in October to an alternative municipal source, and the system was flushed again. Water samples taken during the same month indicated that iron concentrations downstream from the steel pipes were higher than iron concentrations in the incoming water. Water discoloration continued, changing from rust to dark black. The system was flushed again in December, but flushing had to be suspended when the sump pump failed. Additional water samples were taken for analysis.
Water consultants recommended that a corrosion inhibitor be introduced into the system with an injection pump; this was installed in July 1998. The system low points were then drained several times and sterilized. After this process, analyzed test samples from the site fell into acceptable water chemistry ranges. The system then underwent a 14-day process of flushing. During this period, the corrosion inhibitor usage was monitored. After the flushing, the daily maintenance schedule included moving water through the pipes twice a day until the building became occupied.
Despite these measures, discolored water still posed a problem, especially from some little-used faucets. Water samples from the hospital copper plumbing system showed unacceptably high levels (established by the Lead and Copper Rule under the provisions of the Safe Water Act of 1997) of copper (1,810 ppb, max. allowable 1,300...