Key for maps

Sewer key

Water type Origin Colour
Foul water Kitchen, bathroom and trade waste Brown
Surface water Roof, yards and roads Blue
Combined Both foul and surface water Red
NB. Arrow shows the direction of flow

Water key

Water main Origin Colour
Trunk main A main that feeds an area Red
Water main Part of the distribution network to properties Blue
Non potable water Untreated water from reservoirs Dark green 
Proposed mains Proposed water mains Light green

Converting eastings and northings to grid squares

The table below displays the conversion of all the eastings (X) and northings (Y) to a grid square throughout United Utilities geographical area.

Easting (X) Northing (Y) National Grid Square
2 5 NX
3 5 NY
3 4 SD
3 3 SJ
4 SK
4 4 SE

If you had a grid square of SD19 70 12 to convert it to a grid reference, you would change it to: 319100,470200.

A grid reference of 365 321, 342 518 would become SJ65 42 35 after being converted to a map sheet reference (the 21 and 18 are left out as they have no relevance to a grid sheet).


Adoption of sewers

Adoption of sewers transfers to the Sewerage Undertaker the ownership of sewers and the obligation for meeting the cost of their maintenance and improvement to meet increasingly stringent environmental standards.

Building Over Agreement

No building is permitted over public sewers or water mains, without a special agreement such as a Building Over Agreement. Any such building might cause damage and would restrict or interfere with the Undertakers rights of access for inspection, repair, maintenance, or renewal.


A sealed tank having no outlet used for the storage of sewage. The cesspool must be emptied regularly and running costs can be substantial.

Combined sewer

A sewer carrying foul water and surface water.

Conveyancing Form 29 or Con 29

A standard form of conveyancing enquiry, normally addressed to the local authority, published by the Solicitors Law Stationery Society Limited. The Conveyancing Form 29 asks standard questions on such issues as Planning, Development, Highways, Smoke Control Orders, etc. It also asks about drainage. Since 1989, the Sewerage Undertakers have been responsible for maintaining records of public sewers.


In the context of this publication an easement is a legal restriction on the activities landowners can undertake on and above an asset, such as a trunk water main. In particular tree planting and building are generally prohibited. Easements have been used when extra powers are deemed to be needed by the water undertaker to protect the asset.

Foul sewer

A sewer used to transport mainly foul sewage to a sewage treatment works. It may also contain surface water from rainfall, when it may be termed a combined sewer.

Pre 1936 sewers

The Public Health Act of 1936 set out a range of responsibilities for the operation and maintenance of sewerage systems but the Act recognised that little was known about existing sewers. Some had been maintained by private individuals and others by local authorities. Some of the costs had been re-charged to the owners, and the location of all these early sewers had not been surveyed and was unknown. The Act acknowledged the different status of these early sewers and made different provisions in respect of them.

Private drain

A sewer in private ownership draining only one property. If there is no cesspool or private treatment works, the drain usually connects with a private or public sewer.

Private sewage treatment plant

Generally a small sewage treatment works (which could be a septic tank) owned and operated by a community, hotel or household. Treatment plants should conform to the same operational and environmental standards applied to the sewage works operated by the water companies. Accordingly the running costs for small plants can be substantial and as environmental standards are raised there maybe a need for additional capital investment.

Private sewer

A sewer in private ownership draining more than one property. Connection to and use of such sewers normally requires private agreement. Rights of drainage or access, or easements to inspect, maintain, repair or replace the private sewer are usually required if the sewer passes through adjoining land outside the control of the property owner. All downstream sections must be properly maintained to avoid flooding with sewage.

Private water supplies

Where a property has no connection to the water mains, a suitable private spring or surface water source may be used. This may require extensive treatment to make the supplies safe and will be subject to examination and control by the local environmental health officer. Approval under the Building Act 1984 for new building work to domestic properties will not be granted unless adequate water supplies and drainage facilities are available.

Public sewer

A sewer vested in and maintained by the Sewerage Undertaker. Members of the public generally have the statutory right to connect into and use the public sewer on offering payment of sewerage charges.

Rising mains

Pipes carrying untreated sewage pumped under pressure. There is no right of connection into them. Section STET declaration: A Sewerage Undertaker may make, or may be asked to make, a declaration that sewers or sewage disposal works already in existence will be adopted and maintained at public expense from a particular date.

Section 104 Agreement

An agreement made between a housing developer and the Sewerage Undertaker under section 104 of the Water Industry Act 1991, for the adoption of sewers the developer intends to build to serve new houses. A bond to guarantee correct performance often supports the agreement by the developer, of his obligations under the agreement.

Septic tank

A septic tank is a settlement chamber, which provides treatment to sewage and drainage waters. Overflow from the tank goes to a soakaway or drainage field or occasionally a sewer. Septic tanks are un-powered. Houses operating them are responsible for the operation, maintenance and occasional emptying of the chamber. Septic tanks function excellently in well-drained land. It is becoming less acceptable to operate a septic tank in low-lying land, particularly near rivers and streams. Any pollution problems precipitated by poorly performing septic tanks may mean they need to be decommissioned, and connections to the public sewer network need to be undertaken.

Sewerage Undertaker

A Sewerage Undertaker is a limited company succeeding the former water authority and appointed by the Secretary of State to carry out the duties assigned to it by statute. These duties include the provision, maintenance and improvement of a system of sewers and sewage treatment works.

Sludge main

A pressurised pipe carrying treated or partially treated sewage sludge.

Soakaway or drainage field

Buried pipes in aggregates that allow treated effluents or surface waters to disperse. They are owned and maintained by the property owner.

Surface water sewer

 A sewer used only for the transport of uncontaminated surface water or rainwater in an area where separate sewerage systems have been provided. This may discharge safely to a local watercourse or to the foul sewerage system for treatment with the foul flows.

Water Service Company

A provider of both sewerage and water services in an area.

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