That's copper corrosion. No harm one. In developed countries and especially US all homes use copper piping till today. The corrosion will stop once one of the ingredient is used up. Like GI/Iron pipes or even stainless steel there is corrosion mainly due to oxidation or cause by oxygen. Water is a universal solvent, it dissolves all things coming into contact with it even glass get dissolved. It is a matter how much been dissolved depending on the material. Sugar, salts for example get dissolves easily. Water can contain minerals like iron, copper, gold all things in the world. Metal and things like glass are in minute quantity. If you think copper is not safe then the plastic pvc pipe is also not save, it get dissolved in water also. Only those people who want to sell you their filter products will tell you it is harmful to health. If that is the case the filter casing itself get dissolved!!! Plus the filter mediums also get dissolved, of course, in minute quantity insignificant to health drinking it. Our body needs all sort of things in minute quantity and our body will wash away excesses. That's what your kidney and liver for. Do you drink? You are killing your liver when you drink too much alcohol. You drink coke?, you drink coffee? even tea. The food you eat, the veg organic or not with lots of chemical from soil. you eat fish? While you are ok because our bodies take care of it all the times unless you take too much of it at once your body and its organs cannot cope.

Anyway, SS is better than copper as 304 SS is rust free (provided got no chippings). Why not many using SS was because it used to be more expensive than copper pipe until now that some smart fello come up with a new thin SS pipe using copper fittings. The SS pipe used to be as thick as GI pipe mainly because it needs thread to make connection. Now with copper connection or fittings thin SS pipe is used and cheaper than copper. (Copper pipe is more expensive than the thin ss is becasuse copper pipe is too soft and has to be thicker. More volume cost more). Moreover, the thick SS like GI pipe is so rigid and difficult to connect and no bending. A SS fittings costs RM4, whereas a pvc fitting cost RM0.40 and a GI fitting cost RM1-2. Copper fittings is as expensive as SS fitting.

BTW, There are copper coil in heater for heat transfer. Also there are copper in women's bodies, the IUD.

Great to hear that. you are most welcome

By the way, if your piping is exactly what I suggested, ie from tank and from direct with non-return valve; from your description, when you on the pump the pump is pulling water both from tanki and direct. The reason I am saying this is because it is good to use the tank water, otherwise the tank water become stale or become dead water. Since water is also drawn from tanki it is constantly being replenished from direct which contain chlorine and it "clean" the tank or sanitized the tank killing micro organism or germs.

Nice sharing

Installation RM300, 6 foot piping RM600. Total RM900 for this kind of heater simple installation!!!

Do you know that installation for a 60 gallon solar heater is only RM600 which includes

1. Two skilled workers with long ladder dangerously take the heater up the roof. Secured the brackets, install and put the 60 gallon tank in position,
2. fix the non-return valves two pieces,
3. one hot and one cold steel stop valves
3. copper piping one cold to tank and one hot to hot inlet (to bathrooms)
4. Connect heater element to power source at the roof.
5. Pressure testing for leak by switching on pump
6. And if pump bought together with solar heater, pump installation is free of charge

So much work and materials.