The city is preparing to undertake improvements to a downtown water main. The estimated $1.1 million project involves cleaning and lining the 16-inch pipe along a mile-long section of Main Street, from Fowle Street to Davis Street, according to Jay Corey, city engineer. The unlined cast-iron pipe was put in place in 1922, and over the years iron and manganese deposits from the water have adhered to the walls of the pipe, narrowing its diameter and harming water quality, Corey said. Contractors will use a mechanical cleaner to restore the pipe to its original condition and then install concrete lining to prevent further mineral buildup. The city planned to open bids from contractors last week. Work is expected to begin in early May and take about three months. Corey said the project will have little impact on traffic, since the pipe is not being excavated. The project comes in the seventh year of a program to clean and line old water mains in the city.