SO postcode district map, Southampton

Where the SO districts sit

7 districts are plotted without a label where labels would overlap; every one is in the table below.

Where SO sits

It falls across Hampshire and City of Southampton.

Water supply across SO

All 25 SO districts are supplied by Southern Water, which is notable at this size: an area with this many districts usually crosses at least one supply boundary, and this one does not.

Southern Water has a hosepipe ban in force from 10 July 2026, covering the whole of SO.

The shape of the SO area

The districts are wildly uneven: SO16 holds 1,542 postcodes around Southampton and SO25 holds 1, a ratio of about 1542 to one. They divide into 123 sectors.

The numbering is not continuous. SO runs up to 97 but has only 25 districts, so 59 numbers are unused:.

Several districts share a settlement, which is a common source of confusion when a form rejects an address: SO14, SO15, SO16, SO17, SO18, SO19 and SO45 all point at Southampton, SO21, SO22, SO23 and SO25 all point at Winchester and SO50, SO53 and SO97 all point at Eastleigh.

What borders SO

SO sits next to PO (Portsmouth) to the south east, SP (Salisbury) to the north west, BH (Bournemouth) to the south west, GU (Guildford) to the north east and RG (Reading) to the north.

Its neighbours run in 5 different directions, so SO is landlocked by other postcode areas on most sides.

SO districts, settlements and water supply

Principal settlement is the town or city each district sits in or nearest to, derived from OS Open Names. It is not the Royal Mail post town, which is licensed data and not published openly. Status is resolved live from each company’s own notice.

Water hardness in SO

Figures are in milligrams per litre as calcium carbonate, the unit UK water companies report in. 1 of 25 districts has a published figure.

Descriptions such as very soft, soft, moderately hard, hard, very hard are the water industry scale: very soft below 75, soft 75–125, moderately hard 125–250, hard 250–375, very hard above 375 mg/l. Your supplier may use a different scale for the same number.

Contains Wessex Water drinking water quality data, via Stream, licensed under CC BY 4.0. Edition 2022-2025, published 1 January 2025.

Hardness is published per census area, not per postcode, so these figures characterise a district rather than measuring one address. They are a scale and taste matter, not a safety one. Hardness data version wessex-water@2022-2025+yorkshire-water@2026.

Download the SO data

No signup, no email wall. GeoJSON carries the district points, the supplier and the live status, so it can be dropped straight into a map.

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District positions are averaged postcode centroids from OS Code-Point Open. They show roughly where a district sits, not where its boundary runs, and are not legal boundaries.

Frequently asked questions