How can I express this concentration in parts per million? Water supplies with dissolved calcium carbonate greater than 500 mg/L are considered unacceptable for most domestic purposes.
To calculate this you'll need this:
500mg = 0.5g
1L water = 1000mL = 1000g (Density of water is 1g/1mL)
(0.5g CaCO3/1000g water + 0.5g CaCO3) x 1,000,000 = 500ppm
This would be 0.001g/1000g = 1ppm
Here is a video discussing another ppm calculation:
Well organized presentation for several conversions are on this site: http://pages.towson.edu/ladon/concas.html