De-zincification of the impellers is common in well pumps. It has more to do with the salinity of the water than with corrosion. The well drillers Forged Steel Valves around here use the same metal and get 7-10 years of service life out of the impeller. It is not economically justified to spend more for the impeller. Bronze is an alloy of copper, tin, zinc, phosphorus, and sometimes small amounts of other elements. Bronzes are harder than brasses. Brass is an alloy having copper (55%–90%) and zinc (10%–45%) as its essential components. The properties of brass vary with the proportion of copper and zinc and with the addition of small amounts of other elements, such as aluminum, lead, tin, or nickel.
In talking to a well driller today, it is more common to experience corrosion of the stainless shaft of the well pump rather than with the bronze impeller. This would be pitting of the stainless steel.
Wells are annually disinfected for a period of 8-24 hours with a solution of 200 to 400 mg/l of chlorine. Again, this is just one time per year disinfection. After 7-8 years of annual disinfections, there will be evidence of corrosion on the pump shaft, not the bronze impeller.
The chlorination of the water supply would consist of approximately 2 mg/l of chlorine and it would be difficult to see how this would affect the bronze when the 200-400 mg/l of chlorine does not corrode the bronze.

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