How deep are public sewers?

How deep are public sewers in the UK?

For the purposes of this article, when we talk about ‘public sewers’ we are talking about sewers owned and/or adopted by the local Water Authority, such as Thames Water, Anglian Water etc. These sewers will ordinarily be in the Highway, i.e. the road, the pavement or the verge. In around 90% of cases we find them to be in the road. And a public sewer can either be ‘foul’, by which we mean that common sewerage is discharged into them, ‘surface water’, by which we mean that rainwater and other ‘run-off’ water is discharged into them, or ‘combined’ which of course means a combination of the two.

Just because a sewer is owned by a Water Authority, it doesn’t mean that it is in the Highway, it can actually be in private property. So you could have a public sewer running through your back garden, and on a lot of old properties they actually do run across the backs of people’s houses, this is most common in council properties (including ex-council properties) and also many old terraced streets dating back to Victorian times, but also up until 1950s and beyond. We have even known instances of new-build estates nowadays having public sewers running through people’s back gardens. To find the location of most public sewers, click here. 

Back to “How deep are public sewers”, we have been doing sewer connections all over the country for 20 years now, and so this article is based on our experience, not from any official statistics from any water authority.

To date, we have never known a foul  public sewer to be less than 1 metre deep. This will normally be at the ‘start of the run’, which basically means where the public sewer picks up the first house. From this shallowest point of course the sewer will get deeper and deeper, but sometimes if the road is falling in the opposite direction, then the sewer will get shallower relative to the level of the road. In the event that a sewer started at 1m deep, but the level of the road was falling towards the ‘start of the run’, then relative to the road the sewer will become shallower.

Conversely, if the road is falling more than the sewer needs to fall (makes sense…?!) then the sewer is going to get very deep, very quickly.

By the way – all sewers have to be in excess of 750mm deep to prevent freezing during the winter months in the UK, but we tend not to ever find them this shallow.

But how deep do they get? Well, from our experience we tend to find them to be between about 1.5m deep and 3m deep. But they can be much much deeper. In Northampton Town Centre they tend to be 5-6m deep. This is because the ground is relatively flat, but with such a dense population and sheer number of properties packed in together, and all in need of a connection to the sewer, the main foul sewers have to fall as the collect more sewerage from each property, resulting in such deep depths. A lot of large towns and cities are the same.

The deepest sewer we have ever known is 7m deep, this was only 6 metres from the River Thames in Richmond. A quick Google search tells us that the River Thames is only 4.5m deep at this point, so the sewer is a lot deeper than the Thames! If you see on the picture it looks to have been about 6m deep when built, but with another 1 m of brickwork added later on.

A lot of these sewers date back to Victorian times, and of course they would have been dug ‘by hand’, with no machinery such as excavators available back then. It’s amazing to imagine a 7m deep trench having been dug by hand.

If you Google ‘deepest sewer in the UK’, then you will come across the Lee Tunnel, completed in 2016. This is over 4 miles long and is over 70m deep in places, and was installed using TBMs (Tunnel Boring Machines) as opposed to the traditional cut-and-cover method of digging a deep trench.

We’ve generally covered ‘foul’ sewers above, and most of that applies to surface water sewers as well. However, surface water sewer by their very nature do not need to fall as much as foul. As they only generally carry water and no solids, the fall on these pipes can be hardly anything at all. For this reason, albeit they start off around the 1m mark, although they get deeper and deeper, they do so at a lesser extent. In any location where there is a foul and surface water sewer running side by side, the surface water sewer is likely to be the shallower of the two, This is good news in the event that you need a connection doing to the surface water sewer, as of course it will be cheaper, the shallow it is.

As and when a new connection is required onto an existing sewer – which we specialise in at JW Clark Ltd – the pipework has to be laid to the ‘invert’ of the existing sewer. So if the sewer is 4m deep for example, and plenty of them are, then the connection we undertake will be 4m deep. It is not possible to make a connection near to the top of a 4m deep manhole and for the sewage to ‘plop’ into the bottom of the manhole, as this causes blockages to the network and the water authorities don’t allow that under any circumstances. And so the deeper the existing sewer, the more costly the sewer connection. A 1.5m deep sewer connection will require that our excavation is made safe whilst the work is being carried, using trench sheets or a ‘trench box’ for example. But to make a 4m or a 6m excavation safe, is a completely different ball game. We can spend literally days, just sheeting an excavation and making it safe throughout. All of this makes a deep sewer connection particularly expensive. 

If you need a sewer connection completing for a new build, or for an existing property where there is no mains sewerage connection, please be sure to contact us as soon as possible. A lot of developers build a house and then make contact with us, when they should ideally be contacting us prior to starting a project. We even have regular customers of ours who consult us prior to buying a plot of land. If a sewer connection is going to be particularly deep, or if the sewer is a long way from the site, then sometimes this makes it cost-prohibitive to build a new property.

See our fact sheet here which details why you should give us as much notice as possible when you need a sewer connection completing. 

Use our Contact Us form here for a new sewer connection. 

See here for an explanation of how to find the location and depths of existing sewers.

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Guide to downloading Wastewater Asset Plans for Anglian Water & Severn Trent

(For Thames Water Asset Plans please Click Here), and start by clicking the green ‘Register Now’ button on the right hand side of the first page you come to. (Top tip – it’s generally £60 for their standard 5-day service and £120 for their express 1-day service – but we find that if you choose ‘standard service’ it still tends to come within 24 hours!)

For Anglian Water & Severn Trent asset plans, go to www.utilities.digdat.co.uk. At the top of the page, on the far right-hand side click ‘login’. Or ‘Register’ if you
haven’t done so before – it only takes 2 minutes! Click ‘Maps’ at the top right hand side 

Enter the site address, or if this is a new site then
enter the nearest address to your site. Click search and click on the relevant address that comes up below, to continue.

On the map that comes up, make sure your site is within the area displayed. You will now have 3 or 4 options to buy different products, depending on location. Click ‘Buy’ in the green box next to the ‘Wastewater’ option.

In the first field named ‘Title’, enter the name of the plot – this is just for your own reference. Further down next to ‘Manhole Report’, make sure this box is ticked! (Please note that some customers may wish to also purchase the Clean Water drawing – although we will never need this ourselves to quote for your sewer connection)
Click ‘confirm’ at the bottom to continue

Click ‘Proceed to Checkout’

Click the little box at the bottom to agree to Ts & Cs, and then click ‘Next’ at the bottom right

Enter payment details on the final page and you’re done! The drawing should be delivered to
the email address you entered when you first registered. Page 1 will normally be a drawing
showing the various assets in that area, foul water and surface water. On page 2 you may or
may not have some helpful information showing the depths of manholes etc. In any case, this
is the drawing we need! Please email us this drawing for us to be able to quote for your sewer
connection. If you struggle with any of the above, please let us know and we’ll help you as
best we can.

NEW: JWC now provide a service whereby we download a drawing on your behalf. Of course it’s cheaper to do this yourself, but for £80+VAT we can do this for you, and this includes paying the required fee. Click here to use this service.

Beware….! In some instances the asset plan that you download will not show any sewers at all. But the Digdat system will still allow you to purchase and download a drawing for that particular area. And to confuse things even more, the fact that there are no sewers indicated on a drawing, does not necessarily mean that there aren’t any, it just means that the Water Authority don’t have a record of them. The main reason for this is that over time, the government has forced Water Authorities to take on and adopt more of the sewer network as their own, with pipes that were once private and unadopted (including those in the Highway) later on becoming the property of the Water Authority. However, when it comes to public sewers in the Highway, we estimate that about 90% of drawings you download, will show an accurate record. If you need any help interpreting a Water Authority Asset Drawing, then please don’t hesitate to talk to us.

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Terms & Conditions relating to sewer connection quotes

Inclusion of fees in our quotes

In any initial quote that we give, we will list fees that we expect to incur from Highways and water authorities alike. For Example we may quote £400 for a Section 50 and £350 for a Section 106. These figures should be reasonably accurate and will normally be based on our previous experience with different councils and different water authorities. However, due to the many different authorities we deal with, constantly changing fees, and the sometimes quite flexible nature of fees charged by these authorities, our estimates will not always be precise. Having listed a fee of – for example – £400 in our quote, if and when we put our applications in and we are alerted to a higher fee than that quoted to the customer, then these extra costs will be notified to the customer**

Sewer Connections - Building-Site-Scene - JW Clark

Bond payments. 

Our Fact Sheet here explains bonds in further detail.We will not always know at the quoting stage whether or not a bond will be requested from us, by Highways, and we will never know the exact amount, with this being confirmed later on at the consultation stage between us and Highways, after the Section 50 application has been submitted. 

Quoted depths of public sewers

On all quotes for sewer connections, we will always quote the maximum depth of sewer. This will be the invert level of the sewer. We will ascertain the depth of a public sewer by a variety of means including:

  • Information from public records/water authority asset plans
  • Information given to us by our customer
  • Site survey

A site survey will normally be carried out prior to us starting on site, but even in the event that we do a site survey, we won’t always be able to confirm depth of the sewer by lifting manhole covers etc. Sometimes we won’t be able to lift manhole covers prior to traffic management being on site, sometimes our representative who comes to site won’t be able to lift a manhole cover on his own etc. 

In the event that we come to carry out the work and a sewer that we expected to be 2m deep is, for example, 2.2m deep, then the extra dig depth, time involved, extra muck away and extra materials etc, will be charged as extra, with the customer given as much notice as possible. 

Existing pipe materials & sizes

We will always assume public sewers to be ‘vitrified clay’ pipes, unless a Water Authority drawing details them to be another material, for example ductile iron, or MDPE etc. In the event that a public sewer pipe is not marked as being a material other than clay, and it turns out to be another type of material, then the extra cost as a result of this, will be chargeable to the customer** Examples include an asbestos pipe, not marked as such on a drawing. We will also assume the pipe size on a Water Authority drawing to be correct. If the size of the pipe is different then the extra cost will be chargeable to the customer. Both the pipe material and size may be confirmed at a site meeting prior to works starting, but this is not always possible. For example, if we have quoted for a junction insertion on a 225mm pipe, and the pipe turns out to be 300mm, the extra cost in this instance for materials alone, is £300

Traffic management type & associated fees

At the time of quoting we will always quote the type of traffic management we expect Highways to require, for example ‘Give & Take’ or ‘2-way traffic lights’ etc. We are unable to take advice from Highways in advance of submission of a Section 50 to Highways, as the fee we pay them as part of the application is for them to engage with us and often to meet us on site etc. As and when Highways require a higher level of traffic management than we have allowed for, these extra costs will be communicated to our customer**

In a few very exceptional cases, Highways will make changes to what they require from us, part way through the works being carried out. Examples include for traffic lights to be upgraded from 2-way to 3-way, or for the traffic lights to be ‘manually-controlled’. To manually control lights can be particularly expensive, and can cost anything from £350-£450/day. Any such extra costs will always be chargeable to our customer, and of course once on site it is too late for the customer to cancel their order.

Water Authority sign-off

When a sewer connection is completed, this will usually be inspected by the Water Authority (WA) and a ‘sign-off’ of some sort issued, whether it be by email or on their online portal. And of course we repect that our customer will want to see this prior to making final payment to us. Most WAs will require that not only the connection be done and passed before the sign-off is issued, but they will usually require the demarcation chamber to be in as well, and to have been inspected. In most instances we do not fit the demarcation chamber, our customer will normally take care of this. In the event that we do not cover fitting of the demarcation chamber in our quote, and this has not been installed when the WA come to inspect our connection to the public sewer, the job as a whole will not be signed off by the WA, and a second inspection will be required at a later date. Our sewer connection quotes will usually detail ‘payment on completion’, and despite the job not having been signed off by the WA – in the event that our customer has not yet installed the demarcation chamber – these payment terms will still stand and we will still  expect payment on completion.   

Building Control sign-off

Building Control (BC) will rarely be concerned with the connection onto the public sewer, but will sometimes be concerned with the lateral pipework. In the event that this needs inspecting, it will be our customer’s responsibility to arrange inspection by BC, as the person who appointed BC.

Adoption of pipework by water authority

Under a Section 106 connection to the public sewer, the water authority will always adopt the connection onto their sewer. This may be by way of junction insertion, saddle or construction of new manhole. The pipework between the connection and private property (also known as the ‘lateral’) will not normally be adopted, regardless of the fact that it is often in the Highway. Whether the lateral is adopted, or not, is dependent on many factors, including which Water Authority the S106 approval comes from:

Anglian Water will not ordinarily adopt the lateral under a S106 agreement, unless an extra fee is paid. We will always assume our customer does not wish for the lateral to be adopted, unless we are told otherwise** 

Severn Trent will normally adopt the first 15 metres from the connection point under a Section 106 agreement**

Thames Water will not normally adopt the lateral under a S106 agreement 

**Even in the event that the Water Authority is willing to adopt some or all of the lateral, this will be normally be subject to their main criteria that the pipework is laid without any bends; water authorities tend not to allow bends on their network. As we are laying pipework amongst other services in the Highway, it is quite common that a slow bend may be required on pipework we lay, which will prohibit adoption. In the event that pipework must be adopted, we require clear instruction of this at the start of the quoting stage.

For laterals to be adopted properly, the best way to achieve this is with a Section 102 or a Section 104, these must be completed by our customer, we cannot act as agent and apply for a S102/S104.

Zonal charge 

In addition to the cost of a Section 106, there is sometimes a charge from the water authority to the end user, sometimes referred to as a Zonal Charge or an Infrastructure Charge. This is often in the region of £400-£500 and is normally charged as part of the continual billing process between the water authority and the end user, soon after the connection is made. However, occasionally they will invoice us prior to the connection being made, and it may sometimes be sent to us during the Section 106 application. Whether this charge is invoiced directly to the customer after the connection has been made, or to us during the Section 106 application process and in advance of the connection having been done, this charge will never be included in our quote.

Case Studies

For most jobs that we do, we like to do a case study afterwards for our website, see here. The case study is just a brief description of the works, and will normally include some pictures of the works before, during and after. We will never include any pictures of our customer or any other individuals other than our own employees, and we will always be very selective of pictures taken on private property. We will normally give an indication of the value of the work and we will quote the name of the town or village, but won’t ever be more specific than that. We will normally quote the name of the company we are working for, but in the case of a private individual, we will simply refer to the customer as ‘private individual’. If you do not wish for us to compile a case study of work we do for you, please let us know prior to the job being completed. If you’re okay for us to do a case study but would rather some aspects be kept private, for example the value of the works, or the location etc, then please let us know. Even having published a case study, it is not too late for us to change something in the case study, or to remove certain pictures, or information, just let us know.

Payment Terms

Our payment terms will always be detailed in the email body of the original quote, and will normally be ‘payment on completion’. In the event that the value of the job is in excess of £10,000, we will normally request interim payment(s) to be made throughout the works. In the event that an interim payment is not made on time, we reserve the right to stop the works, indefinitely if required, if payment is not forthcoming. The customer in this instance will be liable for the cost of any works carried out but not completed.

In the event that final payment is not made as per our terms, the pipework and the connection to the public sewer will remain the property of JW Clark Ltd. And we reserve the right to either remove pipework laid, both in the Highway and in private property and/or to fill our pipework with cement slurry to put the pipework permanently beyond use. And in order to fill pipework with cement slurry we reserve the right to access the demarcation chamber whether it be in the Highway or in private property, and our customer agrees to this as part of agreeing to our Terms & Conditions.

**As a job progresses, if costs rise and the customer wishes to cancel their order with us, they can do as long as we have not started on site. In the event that fees have been paid to us by the customer, and these fees have been handed over to, for example, the Water Authority or to Highways, we do tend to be able to reclaim these fees back. In the event that the Water Authority or Highways are unable or unwilling to refund us,we will always refund our customer up to a maximum amount of £500 for each of these two authorities.

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