Galvanized pipe used to be very common on domestic water piping system but there are a few issues with using that for domestic water. Galvanized pipe contains Lead which causes problem for human health and it rust easily in contact with soil. Copper is soft and easily bent and it does not react with water and it is naturally lead-free material. Copper is impermeable and biostatic and contaminants cannot penetrate it, and it inhibits the growth of harmful bacteria. Copper is rigid, it won't sag over long runs and requires few supports.
Copper tube and fittings won't embrittle with age, no cracking or crumbling years after installation. Copper will last a minimum of 50 years and is available in three basic types; Type M, Type L, and Type K.
Type M: is a thin-walled pipe. It is the most common type of copper pipe sold and is used mainly behind walls inside homes to route water from the service line and water heater to the fixtures. Trunk lines are typically run in 3/4" type M copper with 1/2" type M branching to serve individual fixtures.
Type L: (hard or soft) is a thicker-walled pipe and is considered standard piping for water services both inside and out. Wherever copper piping will be exposed, type L should be used.
Type K: (hard or soft) is the thickest-walled pipe and is used mainly between water mains and the meter, for heavy-duty vacuum pump lines, and underground lines.