Non-Detect
Definition
A reporting convention for measurements below a method’s detection limit, such as feedwater hardness below 0.5 to 1.0 mg/L. Results are reported as less than the limit, never as zero.
Boiler feedwater hardness is treated as non-detect, typically below 0.5 to 1.0 mg/L as calcium carbonate depending on pressure and design. Because softeners are never perfect, reporting less than 0.5 rather than zero keeps records honest and protects the water treater if a customer later finds a deposit. It reflects the limits of field test kits.
Related concepts
Part of The Blueprint of Water · 📏 measurement