The potential effects of ion exchange softening on the corrosivity of household plumbing materials can be divided into three possible areas. First is the potential effect of a direct increase in the metallic corrosion byproducts. The second potential effect is a change in the chemical characteristics of the water that would either remove or alter film forming constituents in the water. The last one, that is very difficult to achieve with short term testing, is the potential for producing reversible changes in passivation surface films of aged plumbing systems. A research plan was developed to conduct two studies using two different water qualities at the City of Cincinnati Bolton Water Treatment Plant. One study was to be conducted on a finished tap water that had a total hardness of near 160 mg/L as CaC03 and a pH of 9.1-9.3. The second study was to be conducted on untreated groundwater (well water) that had a hardness of around 330 mg/L as CaC03, about twice the hardness as the finished tap water, and a lower pH of 7.1-7.3. This report presents the test results of the first phase on the finished tap water.