The use of reporting water analyses in ppm CaCO3 dates back the the days of steam locomotives. In those days it was wet chemistry using burettes and few had the time or mental capacity to convert the results into the various ions. What the test results measured was effectively millimols or milliequivalents depending on your preference. As CaCO3 has 100 molecular weight this made the maths simple so nearly all the main constituents ( Ca, Mg, Na, Cl ,SO4 ,and CO3 were reported as CaCO3 ( meaning equivalent).To some it might sound cumbersome but when you did not have calculators, just a ready reckoner ,it made life simple. Most of the water treatment companies still use this methodology to this day.
It would appear that the BS uses this terminology, which unless you are familiar with the methodology is a recipe for confusion (no pun intended). I follow Eric's line of thought. Do a bit of homework and do some reading then you will not need BS or anything else. Most of all you will better learn what you are actually doing and soon see through erroneous results.
(That's water to the rest of us!) Beer is about 95% water, so if you want to discuss water treatment, filtering etc this is the place to do it!