SL postcode district map, Slough
Supplier statuses last checked .
The SL postcode area covers 12 districts and 10,672 live postcodes, from SL0 to SL95. It is centred on Slough and also covers Maidenhead, Windsor, Marlow, Bracknell and Gerrards Cross.
Districts here average 889 postcodes.
Where the SL districts sit
2 districts are plotted without a label where labels would overlap; every one is in the table below.
Where SL sits
It is administratively fragmented, reaching into Buckinghamshire, Windsor and Maidenhead, Slough and Bracknell Forest and 0 other authorities.
Water supply across SL
All 12 SL districts are supplied by Affinity Water. That makes SL simple in a way many areas are not: one company, one set of rules, one status to check.
Affinity Water has a hosepipe ban in force from 11 July 2026, covering the whole of SL.
The shape of the SL area
The districts are wildly uneven: SL6 holds 2,316 postcodes around Maidenhead and SL95 holds 23, a ratio of about 101 to one. They divide into 58 sectors.
SL6 alone holds about 22 per cent of every postcode in SL,.
The numbering is not continuous. SL runs up to 95 but has only 12 districts, so 84 numbers are unused:.
District by district: SL0 serves Slough, SL1 serves Slough, SL2 serves Slough, SL3 serves Slough, SL4 serves Windsor, SL5 serves Bracknell, SL6 serves Maidenhead, SL7 serves Marlow, SL8 serves Marlow, SL9 serves Gerrards Cross, SL60 serves Maidenhead and SL95 serves Slough.
Several districts share a settlement, which is a common source of confusion when a form rejects an address: SL0, SL1, SL2, SL3 and SL95 all point at Slough, SL6 and SL60 all point at Maidenhead and SL7 and SL8 all point at Marlow.
What borders SL
SL sits next to UB (Ashford) to the east, TW (Sunbury-on-Thames) to the east, HA (Bushey) to the north east, HP (Hemel Hempstead) to the north and KT (Esher) to the south east.
Its neighbours run in 4 different directions, so SL is landlocked by other postcode areas on most sides.
SL districts, settlements and water supply
| District | Principal settlement | Water company | Hosepipe ban status |
|---|---|---|---|
| SL0 | Slough | Affinity Water / Thames Water | Ban in force |
| SL1 | Slough | Affinity Water / Thames Water | Depends on your supplier |
| SL2 | Slough | Affinity Water / Thames Water | Ban in force |
| SL3 | Slough | Affinity Water / Thames Water | Ban in force |
| SL4 | Windsor | Affinity Water / Thames Water | Ban in force |
| SL5 | Bracknell | Affinity Water / Thames Water | Ban in force |
| SL6 | Maidenhead | Affinity Water / Thames Water | Depends on your supplier |
| SL7 | Marlow | Affinity Water / Thames Water | Depends on your supplier |
| SL8 | Marlow | Affinity Water / Thames Water | Depends on your supplier |
| SL9 | Gerrards Cross | Affinity Water / Thames Water | Ban in force |
| SL60 | Maidenhead | Affinity Water / Thames Water | Depends on your supplier |
| SL95 | Slough | Affinity Water / Thames Water | Depends on your supplier |
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 SL
No water company covering SL publishes hardness figures as open data. The gap is named per district below so you know who to ask.
| District | Hardness | As published | Supply zone | Published by |
|---|---|---|---|---|
| SL0 | Not published by Affinity Water. Check with your supplier. | |||
| SL1 | Not published by Affinity Water. Check with your supplier. | |||
| SL2 | Not published by Affinity Water. Check with your supplier. | |||
| SL3 | Not published by Affinity Water. Check with your supplier. | |||
| SL4 | Not published by Affinity Water. Check with your supplier. | |||
| SL5 | Not published by Affinity Water. Check with your supplier. | |||
| SL6 | Not published by Affinity Water. Check with your supplier. | |||
| SL7 | Not published by Affinity Water. Check with your supplier. | |||
| SL8 | Not published by Affinity Water. Check with your supplier. | |||
| SL9 | Not published by Affinity Water. Check with your supplier. | |||
| SL60 | Not published by Affinity Water. Check with your supplier. | |||
| SL95 | Not published by Affinity Water. Check with your supplier. | |||
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 SL 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.
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
How many postcode districts are in the SL area?
There are 12 SL postcode districts, running from SL0 to SL95, and they contain 10,672 live postcodes across 58 sectors.
What towns does the SL postcode area cover?
SL covers Slough, Maidenhead, Windsor, Marlow, Bracknell and Gerrards Cross. The area takes its name from Slough, and each district is listed with its settlement in the table on this page.
Which water company supplies SL postcodes?
Affinity Water supplies all 12 SL districts. Supply boundaries follow the pipe network rather than postcode geography, so confirm against your water bill if you are near the edge of the area.
Why do SL0 and SL1 both say Slough?
SL0, SL1, SL2, SL3 and SL95 all serve Slough, covering different parts of it. A single town routinely needs more than one postcode district once it passes a few thousand delivery points, so this is normal rather than an error in an address.
Can I download a free SL postcode map?
Yes. This page offers the SL districts as GeoJSON, CSV and SVG, free and with no signup or email address required. The GeoJSON carries each district's position, its water company and its current restriction status, so it can be dropped straight into a mapping tool.
Why is the SL area called Slough when it covers Maidenhead?
SL takes its letters from Slough, where the sorting office that served the area was based when the code was allocated. Maidenhead is the largest settlement in the area today, in SL6, but the area code follows the historic sorting geography rather than current population.
Which councils cover the SL postcode area?
SL reaches into Buckinghamshire, Windsor and Maidenhead, Slough and Bracknell Forest. A postcode area is not a council area: they were drawn for different purposes and a single district can sit across a council boundary, so your postcode does not tell you which authority you pay.