Sewer Connection Cost Calculator — S106, Build-Over & Bond Fees

Section 106 of the Water Industry Act 1991 gives property owners the right to connect to the public sewer, subject to conditions. The water company must be given 21 days notice and will specify the connection point, method and any conditions. A fee is charged for the application and supervision.

If you are building within 3 metres of a public sewer, or directly over it, you need a build-over agreement from the water company. This ensures your building works do not damage the sewer or prevent future access. A CCTV survey before and after construction is usually required.

Some water companies require a bond (financial guarantee) for larger connections or development work. This is refundable once the works are completed satisfactorily and the final inspection is passed. The bond amount varies but is typically £1,000-£5,000.

The water company fee for a standard S106 connection is typically £200-£500. Add to this the contractor cost for the physical connection work (typically £1,500-£3,500 depending on depth and road/footpath reinstatement). Build-over agreements add roughly £150-£600+ for the agreement, with extra legal costs (often £1,000+) for larger-diameter sewers. Always check your water company’s current Scheme of Charges, which is revised on 1 April each year. These are indicative ranges, not fixed prices.

It depends on the property. Connection and civil-engineering works carried out in the course of constructing a new dwelling are zero-rated for VAT, because they are closely connected to the zero-rated construction of the building (VAT Notice 708, section 3; the zero-rate is in Group 5 of Schedule 8 to the VAT Act 1994). So you should not be charged 20% on the connection works for a genuine new-build. A connection to an existing property, or to a commercial/industrial property, is usually standard-rated at 20% — though a connection that is ancillary to a zero-rated supply of water by the same undertaker can itself be zero-rated (HMRC VWASS5200), and a few sewerage undertakers (for example Welsh Water) do not charge VAT on sewerage at all. A refundable security bond is not consideration for a supply, so it sits outside the scope of VAT (HMRC VATSC06120) and is excluded from the VAT base. Use the "Property Type (VAT)" selector above to apply the correct rate, and confirm the liability with your water company or accountant.

Only if your area has a combined sewer system. In areas with separate sewers, surface water must connect to the surface water sewer or be disposed of via SuDS (soakaways, permeable paving). Your water company sewer map will show which system serves your property. Use our Surface Water Drainage Calculator for surface water design or Soakaway Crate Calculator for SuDS options.

The total sewer connection cost has two parts that are easy to confuse. First is the water company’s administrative fee — the Section 106 consent-to-connect charge (typically around £110–£330 per connection; for example Thames Water charges £330 for a direct connection and £110 for an indirect one), plus any build-over agreement, bond or inspection fees. Second is the physical groundwork — excavating, laying pipe, breaking into the public sewer and reinstating any road or footpath, which a contractor carries out and which usually costs from around £1,000 to several thousand pounds depending mainly on the distance to the sewer, the depth and whether the dig crosses an adopted highway. This calculator covers the water company fee side; budget the groundwork separately. Always check your own water company’s current Scheme of Charges, which is revised on 1 April each year. These are indicative ranges, not fixed prices.

Under Section 106 of the Water Industry Act 1991 you have a legal right to connect to the public sewer, but you must first give the sewerage undertaker (your water company) notice of your proposals. The undertaker then has 21 days from receiving your notice to refuse the connection — it can only refuse if the mode of construction or condition of your drain or sewer does not meet the standards it reasonably requires, or if the connection would be prejudicial to its sewerage system (Section 106(4), Water Industry Act 1991). If it does not refuse within 21 days, you may proceed. In practice water companies ask you to apply on their own form and book a supervised connection, so allow a few weeks beyond the statutory notice period. Connecting without consent, or in breach of the conditions, is an offence under the Act.

You can usually build without a build-over or build-near agreement only if you stay more than 3 metres from a public sewer and more than 1 metre from a public lateral drain. Build within those distances — or directly over the pipe — and you need the water company’s consent (Thames Water build-over guidance, in force 2026). Fees are banded by sewer size: for example Thames Water charges around £130 for a Class 1 sewer (internal diameter 175mm or less), £490 for Class 2 (176–350mm) and £585 for Class 3 (over 350mm) plus legal costs starting at £1,000. A CCTV survey of the sewer before and after construction is normally required, and larger or diverted sewers may need a refundable cash deposit. Check your own undertaker’s current charges, as bands and prices are revised on 1 April each year.