boreholes

[Only]

Not for CaCO3. That’s 100g per mole, against 18g for water. There’s roughly a factor of five difference.

You've lost me on that 1

 

[som farmer]

we test for every red tractor inspection, never had a problem, we were on a spring resovoir for years as an old borehole went dry after someone dug a well (before my time). we no longer have an easy mains supply, so every thing is borehole, having ddrunk itt for 60 odd yyyyrs its ffineee

 

[Highland Mule]

Basically, different atoms and compounds weigh different amounts. A calcium carbonate molecule weighs five times more than water molecule, so if they are in a molecular ratio of 1,000,000 water:1 calcium carbonate (ie 1ppm by molecule), the weight ratio will be 200,000:1. As a litre of water weighs a kilo (1 million milligrams), then 1 ppm of CaCO3 by molecular ratio will be 5mg/l in water.

That said, ppm is not a precise unit and could be interpreted in more than one way - albeit the way I have explained would be the “correct” one, chemically.