Use one consistent unit before comparing your water report, test result and equipment specification.
The reference unit
UK consumer guidance commonly expresses total hardness as mg/L of calcium carbonate, written mg/L CaCO3. Parts per million is numerically equivalent to mg/L for this purpose in ordinary water comparisons.
Other units
Reports and equipment may use degrees Clark, French degrees or German degrees. Convert both values to mg/L CaCO3 before deciding whether a system is correctly sized.
Supplier report or home test?
A supplier report represents the relevant supply zone and is the sound first reference for mains water. Drop tests can be useful for commissioning or checking treated water when performed correctly. Test strips are convenient but usually provide a broader range.
Avoid false precision
Water sources and blends can change. Treat a single result as a decision input, not an immutable property of the address. Ask the supplier about unusual variation and follow the test manufacturer's instructions.
Sources and further checks
Sources are provided for verification. Product specifications and local supply information can change, so check the current primary source before acting.