The grain per gallon (gpg) is a unit of
water hardness
Hard water is water that has a high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicar ...
defined as 1
grain
A grain is a small, hard, dry fruit (caryopsis) – with or without an attached husk, hull layer – harvested for human or animal consumption. A grain crop is a grain-producing plant. The two main types of commercial grain crops are cereals and ...
(64.8 milligrams) of
calcium carbonate
Calcium carbonate is a chemical compound with the chemical formula . It is a common substance found in Rock (geology), rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skel ...
dissolved in 1
US gallon
The gallon is a unit of volume in British imperial units and United States customary units.
The imperial gallon (imp gal) is defined as , and is or was used in the United Kingdom and its former colonies, including Ireland, Canada, Australia, ...
of water (3.785412
L). It translates into 1 part in about 58,000 parts of water or 17.1
parts per million
In science and engineering, the parts-per notation is a set of pseudo-units to describe the small values of miscellaneous dimensionless quantity, dimensionless quantities, e.g. mole fraction or mass fraction (chemistry), mass fraction.
Since t ...
(ppm). Also called Clark degree (in terms of an
imperial gallon
The gallon is a unit of measurement, unit of volume in British imperial units and United States customary units.
The imperial gallon (imp gal) is defined as , and is or was used in the United Kingdom and its former colonies, including Ireland ...
).
Usage
Calcium
Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
and
magnesium
Magnesium is a chemical element; it has Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 ...
ions present as sulfates, chlorides, carbonates and bicarbonates cause water to be hard. Water chemists measure water impurities in parts per million (ppm). For understandability, hardness ordinarily is expressed in grains of hardness per gallon of water (gpg). The two systems can be converted mathematically.
Measurement of water hardness
According to the Water Quality Association:
* soft: 0-3.5 grains per gallon (gpg)
* moderate: 3.5-7.0 gpg
* hard: 7.0-10.5 gpg
* very hard: over 10.5 gpg
Conversions
*1 gpg = 0.017118061 kg/m
3
*1 gpg = 1 pound per 7000 gallons
*1 gpg = 17.12 mg/L (ppm)
*1 Clark degree = 0.8327 gpg
*1 dGH = 1.042645169 gpg
*1 mg/L (ppm) = 0.058417831 grains per US gallon
See also
*
dGH
References
*
*
* {{Cite web , url=https://files.knowyourh2o.com/Waterlibrary/watermanual/conversion_factors.pdf , title=CONVERSION FACTORS , date=2002-01-29 , access-date=2010-06-22 , website=KnowYourH2O , archive-url=https://web.archive.org/web/20230602085702id_/https://files.knowyourh2o.com/Waterlibrary/watermanual/conversion_factors.pdf , archive-date=2023-06-02 , url-status=live
Units of measurement
Water chemistry