Why is copper used for making water tanks and pipes?

Answer 1

It is more mallable, requires less fitting, and uses less fittings. It is not as labor intensive to install. It doesn't corrode as easily as galvanized pipe or iron pipe, but is does corrode for several reasons.

Copper is attacked chemically (corroded) by water with low ph, high dissolved oxygen, high level of salts dissolved in the water, and corrosion bacteria such as iron or sulfate bacteria. Bacteria attacks are a bigger problem in closed hot water systems. Because it is manufactured with thinner wall thickness it is also much more subject to velocity errosion. It does not resist acid well and is not used in systems that require regular acid cleaning to remove scale deposited by hard water.

Additionally, since the chemical content of domestic water supplies are invariably sampled at the source, the water plant, or from city water mains, and these systems use iron pipe, they don't show high levels of copper in the water. Copper piping raises the copper level in the water, sometimes to unacceptable levels, depending on the size of the system where it is employed.

Copper is not used extemsively to make water tanks. It is too expensive, and too soft, to make tanks that are sufficiently rigid to support themselves and the weight of their contents.