Mineral / ion
Magnesium
The second contributor to hardness, and the one that gives some mineral waters a distinctly bitter edge.
Key facts
- Chemical form
- Mg²⁺
- Typical range
- Soft supplies 1–5 mg/l; hard groundwater 5–30 mg/l; some mineral waters exceed 100 mg/l.
Where it comes from
Dissolved from dolomite, magnesian limestone and magnesium-bearing silicates. Seawater is rich in magnesium, so coastal and saline-influenced waters carry more.
Typical concentrations
Soft supplies 1–5 mg/l; hard groundwater 5–30 mg/l; some mineral waters exceed 100 mg/l.
What it does
- Contributes to hardness at roughly 1.65 times the effect of an equal mass of calcium
- Imparts a bitter taste above about 50 mg/l
- A dietary source of magnesium
- Magnesium salts are more soluble than calcium salts, so magnesium scale is less troublesome
Removal
Removed alongside calcium by ion exchange, reverse osmosis and nanofiltration.
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- British Geological Survey — Groundwater levels, aquifer mapping and baseline chemistry. Open — attribution required · Open Government Licence v3.0
- National Center for Biotechnology Information — PubChem chemical database. Open · US Government work — public domain