Once popular in water supply lines, galvanized steel pipes have several disadvantages, including weak joints, internal rusting, mineral buildup and water contamination. When plumbers installed galvanized pipes in homes, builders thought their zinc coating helped to prevent corrosion. However, as of 2015, plastic and copper water pipes have fewer problems and are much more popular.
Galvanized pipes use cut threads for joints. However, the process of cutting the thread breaks through the galvanized coating and leaves the joint susceptible to rust. The rust and corrosion eventually lead to broken pipes and water leaks.
The zinc coating inside the pipes prevents rust for a while, but the constant motion of water through the pipes eventually wears through their coating and exposes the steel. As the pipe corrodes on the inside, the opening to carry water becomes smaller. As a result, homeowners notice rust and reduced pressure in their water supply.
While zinc resists rust, it reacts with many minerals in the water supply. The reaction causes the minerals to build up inside the pipes and further reduce the amount of water they deliver.
In older homes, many galvanized pipes also contain lead. Lead leaches from the corroded pipes into the water supply, and this contamination makes the water dangerous for a family to consume.