Water-treatment terms and abbreviations

A compact glossary for reading specifications without mixing different measurements.

Hardness, gpg and mg/L

Hardness commonly concerns calcium and magnesium and may be reported as mg/L as calcium carbonate or grains per U.S. gallon. One gpg is about 17.1 mg/L as calcium carbonate. The hardness guide explains classifications and the limits of regional maps.

TDS means total dissolved solids. It is not the same as hardness and is not a complete safety test. A low TDS reading does not rule out every contaminant.

Flow and capacity

GPM describes gallons per minute, while GPD describes gallons per day. Check whether a figure is a service-flow rating, a nominal membrane production rate or another measurement. The test conditions matter.

A softener’s grain capacity is a load, not a flow rate. Ask which operating programme the figure represents and compare the actual salt and water use.

Standards and claims

A standard number does not mean that every product bearing a broad certification statement treats every contaminant. Look up the exact model, listing and reduction claims. See the comparison guide for a record you can keep.

RO means reverse osmosis. POU and POE commonly describe point-of-use and point-of-entry treatment. These labels describe the arrangement or process; they do not replace a model-specific performance claim.