CO postcode district map, Colchester
Supplier statuses last checked .
The CO postcode area covers 16 districts and 13,771 live postcodes, from CO1 to CO16. It is centred on Colchester and also covers Clacton-on-Sea, Sudbury, Wivenhoe, Coggeshall and West Mersea.
Districts here average 861 postcodes.
Where the CO districts sit
1 district is plotted without a label where labels would overlap; every one is in the table below.
Where CO sits
It falls across Essex and Suffolk.
Water supply across CO
All 16 CO districts are supplied by Anglian Water. That makes CO simple in a way many areas are not: one company, one set of rules, one status to check.
Anglian Water has a hosepipe ban in force from 11 July 2026, covering the whole of CO.
The shape of the CO area
CO10 is the largest district with 1,682 postcodes around Sudbury, and CO8 the smallest with 126. The area divides into 70 postcode sectors.
Several districts share a settlement, which is a common source of confusion when a form rejects an address: CO1, CO2, CO3 and CO4 all point at Colchester, CO8 and CO10 all point at Sudbury and CO15 and CO16 all point at Clacton-on-Sea.
What borders CO
CO sits next to CM (Chelmsford) to the south west, IP (Ipswich) to the north, SS (Southend-on-Sea) to the south west, CB (Cambridge) to the north west and RM (Chigwell) to the south west.
CO 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 CO
No water company covering CO 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 |
|---|---|---|---|---|
| CO1 | Not published by Anglian Water. Check with your supplier. | |||
| CO2 | Not published by Anglian Water. Check with your supplier. | |||
| CO3 | Not published by Anglian Water. Check with your supplier. | |||
| CO4 | Not published by Anglian Water. Check with your supplier. | |||
| CO5 | Not published by Anglian Water. Check with your supplier. | |||
| CO6 | Not published by Anglian Water. Check with your supplier. | |||
| CO7 | Not published by Anglian Water. Check with your supplier. | |||
| CO8 | Not published by Anglian Water. Check with your supplier. | |||
| CO9 | Not published by Anglian Water. Check with your supplier. | |||
| CO10 | Not published by Anglian Water. Check with your supplier. | |||
| CO11 | Not published by Anglian Water. Check with your supplier. | |||
| CO12 | Not published by Anglian Water. Check with your supplier. | |||
| CO13 | Not published by Anglian Water. Check with your supplier. | |||
| CO14 | Not published by Anglian Water. Check with your supplier. | |||
| CO15 | Not published by Anglian Water. Check with your supplier. | |||
| CO16 | Not published by Anglian 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 CO 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 CO area?
There are 16 CO postcode districts, running from CO1 to CO16, and they contain 13,771 live postcodes across 70 sectors.
What towns does the CO postcode area cover?
CO covers Colchester, Clacton-on-Sea, Sudbury, Wivenhoe, Coggeshall and West Mersea. The area takes its name from Colchester, and each district is listed with its settlement in the table on this page.
Which water company supplies CO postcodes?
Anglian Water supplies all 16 CO 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 CO1 and CO2 both say Colchester?
CO1, CO2, CO3 and CO4 all serve Colchester, 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 CO postcode map?
Yes. This page offers the CO 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 CO area called Colchester when it covers Sudbury?
CO takes its letters from Colchester, where the sorting office that served the area was based when the code was allocated. Sudbury is the largest settlement in the area today, in CO10, but the area code follows the historic sorting geography rather than current population.
Which councils cover the CO postcode area?
CO reaches into Essex and Suffolk. 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.