Mineral / ion
Bicarbonate
The dominant anion in most fresh waters and the source of nearly all alkalinity. Bicarbonate is the reason hard water scales when heated.
Key facts
- Chemical form
- HCO₃⁻
- Typical range
- Soft supplies 10–50 mg/l; chalk groundwater 200–350 mg/l; some sparkling mineral waters exceed 1,800 mg/l.
Where it comes from
Formed when carbon dioxide dissolves in water and reacts with carbonate rock. The carbonate system links atmospheric CO₂, rock weathering and water chemistry.
Typical concentrations
Soft supplies 10–50 mg/l; chalk groundwater 200–350 mg/l; some sparkling mineral waters exceed 1,800 mg/l.
What it does
- Buffers pH against change
- On heating, decomposes to release carbon dioxide and precipitate calcium carbonate — this is limescale forming
- Contributes a smooth, slightly alkaline taste
Removal
Reduced by reverse osmosis, distillation and by acid dosing during treatment. Not removed by ion exchange softening, which exchanges cations rather than anions.
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