Quick Answer
PPM (parts per million) means one part of a substance per million parts of water — equivalent to milligrams per liter (mg/L) in practical water testing. It is how chlorine, hardness, and other measurements are reported.
Problem
Test results and product claims use ppm without explaining the unit, so the numbers feel arbitrary.
Product Recommendation
Understanding units helps you read water reports. ZOOSHEN publishes validated reduction levels in clear units after testing. See /technical/nsf-177 for how certifications report performance.