Grain Per Gallon – gpg

1/7000 of a pound – normally used in relation to hardness.

Parts per million – ppm

One part dissolved material in one million parts of water. Used as a measurement for iron, manganese, TDS, hydrogen sulfide, chlorides, sulfates and tannins.

Milligrams per liter – mg/l

Same as ppm

Converting gpg to ppm or mg/l

1 gpg = 17.1 ppm

Total Dissolved solids – TDS

The weight of solids, per unit volume of water, which are in true solution. Can be determined by the evaporation of a measured volume of filtered water and determination of the residual weight. A common alternative method to determine TDS is to measure the conductivity of water.

Hardness

A characteristic of natural water due to presence of dissolved calcium and magnesium. Water hardness is responsible for most scale formation in pipes and water heaters and forms insoluble “curd” when it reacts with soaps. Hardness is usually expressed in grains per gallon (gpg), parts per million (ppm) or milligrams per liter (mg/l), all as calcium carbonate equivalent.

Ferric Iron

Iron that is oxidized in water and is visible. Also called red water iron.

Ferrous Iron

Iron that is dissolved in water. Also called clear water iron.

pH

The potential of hydrogen expresses the hydrogen ion activity or concentration. pH is a measure of intensity of the acidity or alkalinity of water on a scale from 0 – 14, with 7 being neutral. When acidity is increased, the hydrogen ion concentration increases, resulting in a lower pH value. Similarly, when alkalinity is increased, the ion concentration decreases, resulting in a higher pH. The pH value is an exponential function so that pH 10 is 10 times as alkaline as pH 9 and 100 times as alkaline as pH 8. Similarly a pH 4 is 100 times as acid as pH 6 and 1000 times as acid as pH 7.