Mineral / ion
Sodium
Present from geology, sea spray, road salt and — importantly — from ion exchange water softening, which removes hardness by substituting sodium for calcium and magnesium.
Key facts
- Chemical form
- Na⁺
- Typical range
- Inland soft supplies 5–20 mg/l; coastal supplies 20–80 mg/l; the EU and UK limit is 200 mg/l.
Where it comes from
Weathering of feldspars, dissolution of halite, marine aerosol deposition near coasts, and saline intrusion in coastal aquifers.
Typical concentrations
Inland soft supplies 5–20 mg/l; coastal supplies 20–80 mg/l; the EU and UK limit is 200 mg/l.
What it does
- Salty taste becomes detectable above roughly 200 mg/l
- Softened water carries additional sodium proportional to the hardness removed — roughly 46 mg/l of sodium for every 100 mg/l of hardness as CaCO₃
- Relevant to people on medically restricted sodium intake, which is why softened water is conventionally not plumbed to the drinking water tap
Removal
Removed only by reverse osmosis, distillation or deionisation. Ion exchange softening increases it.
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