What Is a Soakaway? How It Works & When You Need One

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June 18, 2025

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What Exactly Is a Soakaway? A Complete Guide to Its Operation and Uses

In the intricate world of property maintenance and environmental responsibility, managing surface water effectively is paramount. As urbanisation continues, and with increasingly unpredictable weather patterns, the need for robust and sustainable drainage solutions has never been more critical. Among the most effective and eco-friendly methods for managing rainwater runoff is the soakaway. But what exactly is a soakaway, how does it function, and when might your property in South East England require one?

At Drainage & Plumbing LTD, we pride ourselves on being the trusted local experts for residential and commercial drainage solutions. Our mission is to provide fast, reliable, and professional drainage and plumbing services across all of South East England, including areas like Croydon, Sutton, Wallington, Coulsdon, Banstead, Bromley, Mitcham, Epsom, Reigate, Redhill, Leatherhead, Kingston upon Thames, Wimbledon, Richmond, Caterham, Guildford, Crawley, and Haywards Heath. Understanding key drainage components like soakaways is part of our commitment to keeping your property safe and dry.

What is a Soakaway?

At its core, a soakaway is an underground structure designed to collect surface water runoff, typically rainwater, and allow it to percolate naturally into the surrounding soil. Unlike traditional drainage systems that direct water into public sewers or waterways, a soakaway works by dispersing the water back into the ground. This process mimics natural infiltration, reducing the strain on municipal drainage infrastructure and replenishing groundwater reserves.

Think of it as a hidden reservoir, a void created beneath the ground that temporarily holds excess water from roofs, driveways, and other impermeable surfaces. This water is then slowly released, or “soaked away,” into the earth at a controlled rate. The design is simple yet highly effective, often consisting of an excavated pit filled with rubble, gravel, or more modern plastic crates, and typically wrapped in a geotextile membrane to prevent soil ingress.

Soakaways are a crucial component of sustainable drainage systems (SuDS) and are increasingly becoming a standard requirement for new developments and significant property alterations, especially where connection to a public surface water sewer is impractical or undesirable.

How Does a Soakaway Work?

The functionality of a soakaway hinges on a combination of collection, filtration, and gradual dispersion. Here’s a step-by-step breakdown of the process:

Collection: Rainwater runoff from roofs, patios, driveways, and other impermeable surfaces is channelled via gutters and downpipes into an underground pipe system. This pipe then leads directly to the soakaway.
Initial Settlement (Optional Silt Trap): In some designs, especially for larger systems, a silt trap or catch basin might be incorporated before the main soakaway. This prevents larger debris, sediment, and silt from entering the soakaway itself, extending its lifespan and efficiency.
Entry into the Soakaway Structure: The water flows into the main soakaway chamber. This chamber can be a simple pit filled with permeable material like clean, angular gravel or, more commonly in modern installations, a series of interconnected, high-void plastic crates. These crates are designed to create a large void space, allowing them to hold a significant volume of water.
Geotextile Membrane: The entire soakaway pit, including the base and sides, is typically lined with a geotextile membrane. This permeable fabric serves a critical dual purpose:
- Filtration: It allows water to pass through freely while preventing fine soil particles from entering and clogging the soakaway’s void spaces.
- Separation: It keeps the aggregate or crates separate from the surrounding soil, maintaining the structural integrity of the soakaway.
Percolation and Infiltration: Once inside the soakaway structure, the water begins to seep through the permeable material (gravel or crates) and then through the geotextile membrane into the surrounding soil. This process, known as percolation, depends heavily on the permeability of the ground. The water slowly infiltrates the soil until it is fully absorbed or reaches the natural water table.
Discharge Rate: The rate at which water infiltrates the ground is crucial. A well-designed soakaway ensures that water is absorbed efficiently, preventing the soakaway from becoming oversaturated and backing up. This rate is determined by the soil type and the size of the soakaway.

Modern plastic soakaway crates offer significant advantages over traditional rubble pits, including higher void ratios (meaning they can hold more water for a given volume), easier installation, and consistent performance.

When Do You Need a Soakaway?

Soakaways are not just an optional extra; in many cases, they are a fundamental requirement for effective and compliant surface water management. Here are the primary scenarios where a soakaway becomes essential:

New Build Developments: Current building regulations in South East England and across the UK often prohibit the direct discharge of rainwater from new properties into public foul or combined sewers. Surface water must be managed separately, and soakaways are often the preferred solution, provided the ground conditions are suitable.
Property Extensions or Large Impervious Surfaces: If you’re adding a large extension, building a new garage, installing a significant patio, or laying a new driveway, you’re increasing the impermeable area of your property. This increases rainwater runoff. Local planning authorities will typically require a method for managing this increased runoff, and a soakaway is a common and effective solution.
Addressing Standing Water or Localised Flooding: If you notice consistent puddles in your garden after rain, or if your property experiences localised flooding due to poor surface water drainage, a soakaway can alleviate these issues. It diverts and disperses the excess water, preventing waterlogging and protecting your landscaping.
Replacing Old or Inefficient Drainage: Older properties might have outdated or insufficient drainage systems. A failing or undersized soakaway can lead to drainage problems. Upgrading or installing a new soakaway can significantly improve your property’s drainage capabilities.
Environmental Responsibility: Even if not strictly required by regulations, installing a soakaway is an environmentally responsible choice. It reduces the burden on public drainage networks, prevents combined sewer overflows (which can pollute waterways), and helps replenish local groundwater.
Properties Remote from Public Sewers: For properties not connected to a public surface water sewer, a soakaway is often the only viable option for managing rainwater runoff effectively and compliantly.

Benefits of a Soakaway

Implementing a soakaway system offers a multitude of advantages for both property owners and the environment:

Environmental Sustainability: Soakaways promote natural groundwater replenishment, mimicking the natural hydrological cycle. This is a key principle of SuDS, contributing to a more resilient urban environment.
Flood Risk Reduction: By diverting and absorbing surface water, soakaways significantly reduce the volume of water entering public sewers, thereby lessening the risk of localised flooding and surcharging of drainage systems during heavy rainfall events. This protects your property and contributes to community-wide flood resilience.
Protection of Property Foundations: Excessive standing water near a property’s foundations can lead to dampness, structural damage, and costly repairs. A soakaway diverts this water away, protecting the integrity of your building.
Reduced Strain on Public Infrastructure: By managing rainwater on-site, soakaways reduce the burden on public drainage systems, preventing their overload and the associated risks of blockages and bursts.
Cost-Effective Long-Term Solution: While there’s an initial installation cost, a properly designed and installed soakaway requires minimal maintenance and can prevent far more expensive issues down the line, such as water damage, foundation repairs, or fines for non-compliance with drainage regulations.
Improved Landscaping: Preventing waterlogging can preserve your garden and green spaces, allowing plants to thrive without being drowned.

Key Considerations Before Installation

Before embarking on a soakaway installation, a thorough assessment is crucial to ensure its effectiveness and compliance. This is where professional expertise from companies like Drainage & Plumbing LTD becomes invaluable.

Site Survey & Ground Conditions (Percolation Test): This is arguably the most critical step. A percolation test determines how quickly water drains into the soil. It involves digging a test pit and monitoring the rate at which water dissipates. This test helps determine:
- Soil Permeability: Is the soil suitable for a soakaway? Heavy clay soils, for instance, have low permeability and are generally unsuitable, while sandy or loamy soils are ideal.
- Water Table: The soakaway must be installed well above the highest seasonal water table to function correctly. If the water table is too high, the soakaway will constantly be submerged and unable to absorb additional water.
- Ground Stability: The ground must be stable enough to support the excavation and the soakaway structure.
Location: The soakaway must be strategically placed, adhering to specific setback distances to prevent issues:
- At least 5 metres from any building foundations.
- At least 2.5 metres from boundaries.
- Away from trees and large shrubs whose roots could damage the structure.
- Clear of underground services (gas, water, electricity, communication cables).
Size & Design: The size of the soakaway is not arbitrary. It must be precisely calculated based on:
- Contributing Area: The total impermeable area that will drain into the soakaway (e.g., roof area, driveway area).
- Rainfall Data: Local rainfall intensity and duration.
- Soil Infiltration Rate: Determined by the percolation test. This calculation ensures the soakaway has sufficient capacity to handle peak rainfall events without overflowing. Oversizing is always better than undersizing.
Materials: The choice of materials impacts efficiency and longevity:
- Soakaway Crates: High-strength, modular plastic units are increasingly preferred for their high void ratio and ease of installation.
- Aggregate: If using a traditional design, clean, washed, angular gravel (e.g., 20-40mm) is used to create the void space.
- Geotextile Membrane: Essential for preventing soil ingress and maintaining the soakaway’s function.
Regulations & Planning Permission: In South East England, soakaway installations are subject to building regulations. For new builds or significant alterations, planning permission might also be required. It’s crucial to ensure compliance with all local authority requirements.

The Installation Process (Simplified)

While best left to professionals, understanding the general steps of soakaway installation can be helpful:

Site Assessment & Design: As discussed, this involves percolation tests and calculating the soakaway size.
Excavation: A pit of the determined dimensions is excavated at the chosen location.
Lining: The excavated pit is carefully lined with a suitable geotextile membrane, ensuring sufficient overlap for sealing.
Structure Placement: The soakaway crates are then assembled and placed within the lined pit, or the pit is filled with the chosen aggregate.
Connecting Pipework: The drainage pipework from the property’s downpipes or surface drains is connected to the soakaway.
Backfilling: The soakaway structure is covered with a layer of aggregate (if using crates), then the geotextile membrane is folded over and sealed, and finally, the pit is backfilled with excavated soil, ensuring proper compaction and grading for surface drainage.

Maintenance of a Soakaway

Once installed, soakaways require relatively little maintenance, but occasional checks can ensure their long-term performance:

Regular Inspections: Periodically check the area around your soakaway for signs of waterlogging, slow drainage from downpipes, or subsidence. These could indicate a problem.
Keep Area Clear: Ensure that the area directly above and around the soakaway is kept clear of heavy vehicles, large plants whose roots could interfere, or significant debris accumulation.
Clean Gutters and Downpipes: Preventative maintenance upstream is crucial. Regularly clean gutters and downpipes to prevent leaves, silt, and other debris from entering and potentially clogging the soakaway.
Warning Signs of a Failing Soakaway: If your soakaway is struggling, you might notice:
- Persistent puddles or boggy areas in your garden after rain.
- Water backing up in downpipes or surface drains.
- Foul odours from drainage points (though this is more common with foul water issues).

If you suspect your soakaway is failing, it’s essential to contact a professional drainage company like Drainage & Plumbing LTD for diagnosis and repair.

Why Choose Drainage & Plumbing LTD for Your Soakaway Needs?

When it comes to the intricate world of drainage and plumbing, particularly for critical systems like soakaways, expertise and reliability are non-negotiable. At Drainage & Plumbing LTD, we are dedicated to providing top-rated services across South East England.

Local Experts, Extensive Reach: We proudly serve South East England within a 25-mile radius, including key areas such as Croydon, Sutton, Wallington, Coulsdon, Banstead, Bromley, Mitcham, Epsom, Reigate, Redhill, Leatherhead, Kingston upon Thames, Wimbledon, Richmond, Caterham, Guildford, Crawley, and Haywards Heath. Our local knowledge ensures we understand the specific ground conditions and regulatory requirements unique to this region.
24/7 Emergency Service: Drainage problems don’t keep business hours. Our team is on call 24/7 to handle urgent drain problems quickly and efficiently, any time, any day. This means fast, reliable solutions when you need them most, minimising disruption to your home or business.
Highly Trained & Certified Technicians: Our team comprises skilled drainage engineers who are experienced, fully equipped, and ready to tackle even the toughest blockages and installations. We use the latest technology to accurately diagnose and resolve issues, always adhering to strict industry standards.
Customer Satisfaction Guaranteed: Customer satisfaction is at the heart of everything we do. We go above and beyond to deliver service you can trust, ensuring transparency, clear explanations, and no hidden costs. Our aim is to fix your problem quickly and properly, with a professional attitude and a friendly approach.
Comprehensive Drainage Solutions: Beyond soakaways, we offer a full range of services including unblocking toilets, sinks, showers, and drains, fixing blocked and broken drains, grease and fat build-up removal, general drainage problem diagnosis, drain cleaning, and leak detection. We are your one-stop solution for all drainage and plumbing needs.

Whether you’re planning a new build, extending your property, or simply need to address existing drainage issues like persistent puddles or a failing soakaway, our team is here to help.

Get In Touch With Us Today

Understanding and properly implementing drainage solutions like soakaways is vital for the long-term health and safety of your property. They are a critical component of modern, sustainable drainage systems, helping to manage surface water responsibly and protect your investment.

Don’t let drainage problems cause you stress or costly damage. Our team is ready to assist you with any drainage or plumbing issue, big or small. You can reach out by phone, email, or WhatsApp. We aim to respond as quickly as possible, typically within 2 hours for enquiries.

Contact Drainage & Plumbing LTD today: