Innovative sewer technology to tackle blockages

We are testing new technology in our regions to better understand our sewer networks and prevent incidents before they happen.

The wastewater network is a collection of pipes and infrastructure that take waste from the sinks, toilets and drains in our homes. This waste travels along sewers to treatment sites before being thoroughly treated and safely released into the environment. 

It is important that the contents of the network can flow to keep this process moving. When blockages occur in the network, this can cause waste to stop flowing. With nowhere to go, this waste can then back up into homes or seep out into the environment.

We need to keep our networks performing to the highest standard to deliver the service our customers deserve. This is why we’re investing in innovative new technology for our networks to make them resilient for future generations.

Testing new technology across our region


Sewer blockages are extremely costly and time consuming for water companies to tackle, especially when caused by items that are not suitable for flushing. In 2018, it was estimated that sewer blockages from wet wipes alone cost UK water companies £100m a year to deal with, forming blockages and causing floods which can also impact the environment.

As part of our wastewater network transformation, we're piloting the use of sewer level sensor technology in our region. These sensors monitor the levels of liquid in the sewer. When they show the levels rising unexpectedly, this could indicate a blockage is forming. This could help us alert our teams to intercept and clear the issue before it becomes more serious.

We are trialling over 100 sewer level sensors in a six-month period across our region. Digitising our network in this way enables us to approach the management of our sewers proactively.

This will play an important part in helping us minimise flooding and pollution events.


Over the coming year, we hope to roll out up to 30,000 sensors across our region at no extra cost to Southern Water customers, in specific high-risk areas to target challenges we’ve experienced on our networks.

March 21: Pilot project begins.

April 21: Key worker operational crews head out to install the sensors in pilot areas.

September 21: We review how well the sensors have performed in the pilot and prepare to expand the new digital sensor network across our region.

October 21: Our crews begin to install sensors in key areas across our region.

March 22: Sensors are installed and functioning in key areas, helping us to provide a better service for our customers.

How you can help

It is estimated that around 75% of blockages occur due to the wrong things entering our sewers. Our sewers are only around 200mm in size and should only carry the three Ps – that’s pee, poo and paper.  

The main items that end up in our sewers when they shouldn’t are:

  • Unflushables such as wet wipes, sanitary items, nappies and cotton buds. Wet wipes are a serious problem for our sewer network. Even wipes labelled as ‘flushable’ do not break down in the sewer network. They are the main culprits for blockages.
  • Fat, oil and grease from cooking poured into sinks when hot, which then solidify in sewers as they cool. Instead, you can simply pour used fat, oil and grease into a 'GunkPot' and transfer them to a waste bin when cool. If you don't have a GunkPot, then you can use other recyclable, heat-resistant items to contain these liquids, such as empty cans, heat-safe glass jars or microwave-safe bowls.
  • When fats, oils and greases mix with wet wipes, it can form powerful solid blockages that have become known as 'fatbergs'. These disgusting blockages have been found weighing upwards of 130 tonnes and over 250 metres in length, requiring extensive work and disruption to remove safely.

We're asking customers to help us by only flushing the three Ps and disposing of all other items into waste bins. Along with our new network of sensors, you’ll be playing your part in helping to keep our sewers flowing freely.

Frequently asked questions

What is a “sewer level monitor” or “sewer level sensor”?

Simply put, a sewer level monitor or sensor is a device that measures the depth and sometimes flow of water in our waste network, usually installed underneath manhole covers.  

Using similar technology to your mobile phone, the sensors then send this information back to us so we can get an accurate picture of what’s happening in the sewers beneath your feet. 

Has this been done before?

Yes, but not with the same scope as our work – the scale and pace of our roll-out is one of the most ambitious in the UK. 

Southern Water also has a limited number of sensors already in place across its operational region, but this pilot and eventual roll-out represents a commitment from us to deliver the best wastewater service possible to our customers. 

When will this be happening?

To begin with, the limited pilot of around 100 monitors will take place from April 2021 to October 2021. 

Depending on how the pilot progresses, the full roll-out across our region will then begin with incremental installations of thousands of sensors at a time. 

Where is the pilot happening?

We are running the pilot in key areas across our operational region: 

  • Havant, Hampshire 
  • Hedge End, Hampshire 
  • Rowland’s Castle, Hampshire 
  • Southampton, Hampshire 
  • Waterlooville, Hampshire 
  • Ramsgate, Kent 
  • Fairlight, East Sussex 
  • Hastings, East Sussex 
  • St. Leonards-on-Sea, East Sussex 
  • Barnham, West Sussex 
  • East Grinstead, West Sussex 
  • Lidsey, West Sussex 
  • Walberton, West Sussex 
  • Woodgate, West Sussex 

This list is subject to change, and some areas may be replaced or not deployed to at short notice. 

Why did you select my area?

Your area has been selected for the pilot as we have specifically chosen areas where we might be able to see the clearest picture from the monitors, which will enable us to learn from them before the full roll-out. 

How will this affect me, my house or my area? Do I need to do anything?

You don’t need to do anything. We may need to access your front or rear gardens where manholes serving houses on your street can be found, but you don’t need to do anything differently during the pilot. The sensors will be installed without disruption and without affecting services.  

What data will you be collecting? How will you use it? Can I opt out?

As this is a limited pilot, and we won’t be collecting any data or information about your property specifically, you therefore cannot opt out as we need to monitor the part of the network your property is in. 

None of the data we collect will be tied back to you or your property individually. We will be using the data we collect from the sensors only to improve our wastewater networks. 

Will my bills increase?

This pilot is part of a larger potential investment on sewer level sensors across our whole region over the five years. Your bills will not be affected by the pilot or any planned roll-out of the sewer level sensors in future.

Who owns the sewer connected to my house?

To learn more about the ownership of sewer networks, watch this series of short films that explains about the transfer of private sewers and where responsibility for clearing blockages and maintenance lies. 

Who should I contact if there's a problem?

If you've got a question or are concerned about anything to do with the trial taking place, you can use the contact form link at the bottom of this page to reach us. However, if something is taking place that you consider is in need of urgent response, please telephone our emergency line on: 0330 303 0368.

Get in touch

If you’d like to know more or have any questions about the pilot scheme and future roll-out, please get in touch with us using our contact us form. 

How to prevent blockages

Avoid costly repairs to your home or business by making some simple changes to how you dispose of kitchen and bathroom waste.

Find out more