Southern Water Tap Water Quality

Southern Water supplies South East England with drinking water drawn from chalk aquifers of the South Downs, North Downs, and Hampshire Basin, supplemented by chalk boreholes and surface reservoirs.

Southern Water serves a region underlain almost entirely by chalk — one of the most productive aquifer systems in Europe. This geology drives very high water hardness throughout much of the supply area. Brighton, Eastbourne, and much of Sussex record hardness of 270–310 mg/L. Southampton and Hampshire zones are typically 220–260 mg/L. Southern Water has faced regulatory scrutiny in recent years, including enforcement action related to sewage management and water quality compliance. The company has multiple active PFAS improvement programmes, with near-airport and near-military sources showing the highest PFAS burden.

Typical water profile

With typical hardness of approximately 260 mg/L CaCO₃, water in the Southern Water supply area is classified as hard to very hard. This means significant limescale buildup on kettles, showerheads, and heating elements over time. A water softener or quality filter jug is a worthwhile investment for most households in this area.

Notable: Very hard water across most of the region. Some zones near airports and former military sites have elevated PFAS concern. Active DWI enforcement for multiple improvement programmes.

Is Southern Water water safe to drink?

Yes. All treated water supplied by Southern Water meets the UK Drinking Water Regulations. The Drinking Water Inspectorate (DWI) audits every water company annually — Southern Water serves 4.7 million customers across 76 supply zones. Each zone is tested thousands of times per year and results are published in the annual compliance report.

However, water quality varies significantly between zones within the Southern Water supply area. Your specific zone may have different hardness, nitrate, or THM levels from your neighbour in a different zone. That's why it's worth checking your exact postcode above.

How to check your Southern Water zone

Enter your postcode in the box above to see zone-specific data for your address — including hardness, nitrates, lead, chlorine, fluoride, and THMs — drawn directly from Southern Water's most recent annual compliance report.