What it is
Chloride is the main part of common salt. All water contains some; the amount reflects the rocks the water has passed through and anything that has been added along the way.
Where it comes from
Natural chloride comes from salt-bearing rocks and, near the coast, from sea spray and seawater intrusion into the aquifer. Man-made sources are road de-icing salt, sewage and septic effluent, and the brine from water softeners.
Why it matters
Chloride is not a health concern at the levels found in UK supplies. The guideline is set for taste: above it water tastes salty, and high chloride also makes water more corrosive to metal pipework. A rising chloride result is a useful early warning that something is reaching the source.
What can be done about it
If chloride points to a contamination route, the engineer deals with that first. Where the water itself is salty, reverse osmosis is the treatment that removes it; softeners and ordinary filters do not.
Information last reviewed 5 October 2026 by Pozzani Pure Water.