Unclear on translated terminology. In US, sanitary is typically interpreted as sanitary sewer piping. Water for drinking would be termed potable water. It sounds like OP is asking about potable water due to mentioning mainly using PEX. In US copper was the water piping of choice for decades because it was way better than the only other alternative if galvanized steel. There was a brief period 20 years ago where CPVC battled in the marketplace with copper based. Copper was marketed as the higher quality option. But now I’d say 90% of new plumbing is PEX in most of the US. More on reddit.com

Copper sits in the 11th group of the periodic table, which puts it above silver and gold, which are known for being fairly stable when exposed to water. One could use silver which is a known anti-microbial for plumbing, but this would be jolly expensive. Silver is in the solder that creates the join the same reason. When copper is used in household plumbing, oxidation occurs on the outside of the piping, turning it green. The inside, which is submerged in water, does not undergo oxidation, thus not contaminating your water. Back in the day the romans used to use lead, some water pipes are made out of iron, copper is the best for health reasons. Reason number two, its a brilliant conductor of heat energy. Three, its very easily worked by hand, drawn into complex shapes and soldered to create connections and t-pieces that are permanent, something that couldn't be done with iron or even plastic pipes which are fairly set in shape. Four, alternatives like iron rust, plastic will not stop a rat trying to grind down its teeth for very long, and aluminum whilst a comparable material in terms of workability, is still as expensive, and terrible to try to weld together as it only subtly changes color with greater temperature. Source: Engineer. More on reddit.com

Copper lasts. It outlasts almost all other materials because of its location in the galvanic series. It doesn't react with much of anything. Put another way, it won't rust. It is also easy, even pleasant to work with and the tools needed to cut and join it are simple. More on reddit.com

Aluminum needs an inert gas environment for welds and reacts slightly with water over time. It's not really easier to handle than copper when it comes to joining pieces and would slightly contaminate the water supply fed through it. Since most of us redditors spend our entire lives drinking from plumbed household water supplies, the exposure over time could end up being harmful. More on reddit.com