Thanks to all!
I am beginning to realize that EC/TDS meters do not detect the type or even the content of certain impurities. Resistance of the water doesn't show if organic toxins are a problem or whether the resistance measurement is low due to sodium, calcium, sulfates, potassium or iron, copper or magnesium or lead, hexavalent chromium, cadmium, arsenic or mercury!
It all started when my friend installed a $4000 6-stage RO water filter system and he boasts that it creates structured re-vitalized water that shows <30 micro-siemens of conductivity.
But that obviously doesn't tell the whole story.
I was already frightened. Every time they shut the water off in this 100+ yr old apt building plumbed with iron pipes we have a horror show. When the water is turned back on, the water is mud, dark brown, with hard sediment. Water from the tap slowly sheds it brown color only after several hours. After a day or two, the water is crystal clear to the eye but does have a hard water's nasty taste. If boiled and poured into a glass jar, it will develop a cloudy-white precipitate at the bottom after a day in the fridge.
For the plumbers who do the work, this effect is a cash cow. The sediment clogs and fouls/damages every water valve, be it sink, shower, washing machine or toilet, creating a mountain of new business from tenants who soon complain of low faucet water volume or leaking water reservoir filling valves in the toilets.
If a glass filled with this water is emptied and allowed to dry, the water creates a hard to wash-off cloudy film on the drinking glass.
The water in this area is super hard, lots of calcium and GKW else.
Can drinking unfiltered water from my kitchen cold-water tap, even waiting several days after a repair event, be dangerous to drink?
Or is it a great source for minerals like calcium, zinc and iron in my diet?
The city says on their website that their water is safer than bottled water to drink! But that is before traveling through many pipes to finally get to be super-mineralized by the galv. iron plumbing of my apt building.