Portswood Water Hardness & Quality Report (2026)

Southern Water supplies Portswood in the city of Southampton near the University of Southampton, from the River Itchen — one of England's finest chalk streams — treated at Otterbourne Water Treatment Works south of Winchester, supplemented by Hampshire Chalk borehole abstraction throughout the Itchen valley. At 287.5 mg/L (20.2°Clark) and a TDS of 833.6 mg/L, Portswood's water is very hard, driven by the chalk-saturated Itchen supply that is the defining characteristic of Southampton's historic water quality.

The River Itchen rises in the Hampshire Chalk above Cheriton near Alresford and flows south through Winchester and Eastleigh, receiving constant chalk groundwater discharge along its entire length from the Upper Chalk aquifer of the Hampshire Basin. At Otterbourne, Southern Water abstracts from the Itchen at a point where the chalk aquifer is deep, productive, and extensively confined beneath Reading Beds and other Tertiary strata, producing near-saturated calcium bicarbonate groundwater. The resulting 287.5 mg/L with TDS 833.6 mg/L is the classic character of Southampton's chalk Itchen supply — very hard, highly mineralised, and consistent year-round.

At 287.5 mg/L, limescale is a significant and persistent household challenge in Portswood. Kettles require descaling fortnightly to prevent element damage. The combi-boiler needs a properly fitted scale inhibitor and annual professional servicing to protect the heat exchanger. Washing-up liquid requires considerably more product per wash to achieve adequate lather. Taps, shower heads, and basin mixers develop heavy limescale deposits within one to two weeks; a fortnightly descaling wipe with white vinegar or a proprietary product is strongly advisable. A whole-house water softener is strongly recommended for Portswood households to protect all appliances from this very hard Hampshire chalk supply.