A sump pump is a water pump (usually automatic) that sits inside a sump chamber at the lowest point of a property or drainage system. The chamber collects water and when the level rises the pump turns on automatically and discharges it to a suitable location such as a drain, ditch, soakaway or sewer.
Water should be allowed to flow into the chamber. That might be from a cavity membrane system, channel drains, groundwater or low-level foul or grey water where gravity drainage is not possible.
As the water level rises the float switch on the automatic sump pump rises, the pump starts and the water is discharged through the pump hose. When the level drops the pump stops. That cycle might happen once in a month, or it might happen constantly during a storm depending on what the system has been designed to deal with.
At its most basic you have a chamber, an automatic submersible water pump and a discharge hose. The one fitting that must always be considered is a non-return valve.
The photo below shows a pump that had been supplied by a different company and installed into an existing chamber in a cellar without a non-return valve. The pump would run, pumping the water up 2m out of the cellar, empty the chamber and switch off. All the water sitting in the discharge hose then ran straight back into the sump under gravity, lifted the float and started the pump again. It just sat there cycling on and off. That sort of short cycling destroys pumps and it is completely avoidable. This was replaced by an AMA Drainer 301 Automatic Water Pump which comes supplied with a non-return valve as standard.
The tools required depend entirely on where the sump is going.
Sometimes it is a case of digging a hole with a shovel and concreting the chamber back in.
In other situations you are cutting a floor slab, breaking out concrete and removing spoil through the house. That is when the planning matters because you do not want to create a new route for groundwater while you are trying to solve the original problem, thus extreme caution should be taken. If you're cutting through a damp proof membrane, the installation needs consideration as to a waterproof concrete too.
There are generally two styles of sump chamber.
The first is a Packaged Pump Station. This is a pre-formed chamber supplied with the pump and internal pipework ready to install. If you are starting from nothing this is normally the simplest and most reliable option because you know everything fits and works together, and they are supplied from floodandwaterpumps.co.uk with integrated non-return valves.
The image below shows a packaged pump station complete with the automatic pump, plus the factory-installed internal pipework, including the non-return valve, visible here in white.
The second is a formed sump built on site. These are often created to give access into an existing drainage system or as part of a wider drainage scheme where the chamber size and depth are dictated by the construction, or, they could be a pre-existing chamber in a basement, installed historically.
Examples:
| Feature | Packaged Pump Station | Site-Constructed (Built) Sump Chamber |
|---|---|---|
| What it is | Pre-formed chamber supplied as a complete system with pump and internal pipework | Chamber formed on site or an existing chamber adapted to house a pump |
| Installation speed | Fast and simple installation with predictable setup | Slower, depends on construction method and access |
| Design certainty | All components sized and tested to work together | Pump, pipework and chamber must be selected and configured individually |
| Best suited for | New installations, external works, driveways, flood defence systems, pumped drainage | Existing basements, refurbishment projects, access to existing drainage |
| Structural integrity | Factory manufactured chamber designed for burial | Depends on build quality and materials used on site |
| Depth flexibility | Fixed chamber depths | Can be formed to suit the construction and required depth |
| Pump access and maintenance | Designed for easy pump removal and servicing | Access depends on how the chamber has been constructed |
| Internal pipework | Pre-installed including non-return valve | Installed on site and must be detailed correctly - such as installing an NRV |
| Risk of installation error | Low, as the system is pre-engineered | Higher if pump sizing, float movement or pipework are not set correctly |
| Discreet finish | Designed to take standard inspection chamber covers and sit flush with ground level | Finish depends on how the chamber is formed and covered |
| Suitability for foul systems | Available in larger diameters for sewage and foul pumping stations | Can be constructed for foul, but requires correct benching, sealing and ventilation |
| Integration with drainage | Straightforward connection to new drainage layouts | Often used to connect into existing drainage systems |
| Cost profile | Higher upfront product cost, potentially lower installation cost and less risk | Higher labour and design input for construction, plus materials, concrete etc |
| Typical use in flood control | Creating a dedicated low point behind flood barriers or for pumped outfalls | Retrofitting a pump into an existing cellar or drainage access chamber |
| Long-term reliability | Very high when correctly specified | Highly dependent on installation quality and design |
If the sump is already there the job can be simple, assuming you choose the correct water pump.
You must check the width, the length and the depth of the sump chamber. Not just whether the pump drops in, but whether the float can move freely and whether the on and off levels suit the chamber. A pump that is too tall for a shallow sump will never switch off properly. A float that catches on the wall will not switch on at all.
The image above shows an APP HD-15 Submersible Site Pump - High Flow Rate Water Pump installed with SUCTION/DELIVERY HOSE 80mm (3 inch) used for the discharge hose.
The discharge hose should be reinforced suction and delivery hose or solid pipework.
The image below shows a chamber used as a collection point during a flood with a pump placed in manually. It worked, but it relies on intervention and the layflat hose has kinked, restricting the discharge. With a fixed pump, proper discharge pipework and automatic controls this type of arrangement becomes a fully passive system. Leaving the lid off is not recommended as it creates a safety risk, even though it was being monitored like a puddle pump.
If you are installing a new sump pump, a Packaged Pump Station keeps things simple. You match the chamber size and the pump performance to the job in hand. Flow, head and the type of water being pumped all matter.
Once it is in the ground it needs to be concreted in place to prevent flotation and stop movement.
Inside a basement a sump pump is often part of a Type C waterproofing system, or installed to collect and remove groundwater ingress.
The chamber should be fully concreted in and any excavation through the slab needs to be done carefully. If you open up a new pathway for groundwater you can make the situation worse.
You may see basements where perforated chambers have been installed and surrounded with gravel. It looks like it should work, but in practice you end up pumping groundwater from below the slab level all the time. That costs money to run, it creates a drawdown that pulls more water towards the property and over time you can start moving fines out of the ground which can lead to settlement.
If internal drainage is taken into a sump it should collect water at slab level using channel drains or gullies. Breaking through an existing floor to install land drains beneath the slab and then permanently pumping groundwater is a very different approach. It creates continuous drawdown below the structure, increases running costs and can actually draw more water towards the property. This is different from a designed Type C system installed at construction stage, where drainage is formed at formation level beneath a new slab.
Sumps can be installed to handle grey water from showers, and sinks. Foul installations are another common use where the sewer is higher than the floor and gravity drainage is not possible. In that situation the chamber must be sealed and have a locking lid.
Integral garages are often the lowest point of the house and the first place water enters. Putting a sump pump in the garage floor can be a very effective form of flood resistance and it usually causes far less disruption than digging up the inside of the property.
You often see the same thing in high street shops that rely on flood barriers. If any water gets through, the sump in the floor collects it and sends it back out again.
As always, concrete it in properly and run the electrics in conduit. The installation of course depends on the property’s suitability.
Outside, a sump pump can be used as part of a pumped drainage system, taking flows from channel drains, gullies or foul connections and discharging them to a suitable outfall where gravity drainage is not possible.
A sump can also be installed to form a dedicated low point behind a flood wall or barrier so that water is collected and removed automatically. This avoids the need to deploy puddle pumps on a driveway or hardstanding because the water naturally finds the chamber and the system operates on its own.
At floodandwaterpumps.co.uk, we supply Packaged Pump Stations for this arrangement that are sized to accept a standard inspection chamber cover. Day to day, a normal a lid is fitted so the chamber does not constantly fill during rainfall and the installation remains clean and unobtrusive.
When a flood warning is issued or bad weather expected, this can be swapped for a drilled or open lid, allowing water to enter the chamber and be pumped away. Because the cover is a standard size there are no proprietary parts and replacements can be sourced easily if ever required.
The installation shown below is set into a driveway behind a flood wall. In this location water pools during flood conditions because the surface water system cannot discharge, groundwater levels rise, and there is also direct rainfall and seepage through the structure. By creating a permanent low point the water is brought to a single collection location and removed as it arrives.
The chamber is fully concreted in and finished flush with the paving so in day to day use it is barely visible, as shown in the second image, but during a flood it becomes the control point for the whole area.
In simple terms, it means no pumps to deploy, no trailing hoses and no standing in water trying to manage it during a storm. The system can activate and operate whether you are there or not.
In normal conditions the chamber sits flush with the paving and is effectively hidden from view, so day to day the installation is discreet.
In the right ground conditions, an external chamber can be perforated and surrounded with gravel, with a geotextile between the gravel and the soil. The base must not be perforated and it must be concreted in to help prevent floatation.
Installed correctly this can stop the chamber filling and pump running in normal rainfall because the water disperses back into the ground similar to a soakaway, but in a flood it will still collect and remove water from both the drain and the surrounding ground area.
The image below shows a system being installed in this manner, and it in use behind a flood barrier.
This type of installation should not be close to the house. The same thinking as soakaways applies.
The image below shows a similar set up with a channel drain installed across the driveway and connected into the sump. In normal conditions any water simply disperses into the ground so the pump does not run. Because this is located behind a flood barrier, during a flood it captures seepage, rising groundwater and rainfall, which are then collected in the chamber and pumped away.
The image below shows a packaged pump station during installation. The chamber has been perforated and surrounded with clean gravel to allow groundwater and surface water to enter, with a surface water drain connected. The green suction delivery hose is being laid below ground and will discharge to a ditch away from the area, creating a controlled collection and pumped outfall.
Of course, if a chamber is to be perforated, with holes drilled into the sides to allow groundwater to enter (and exit), the sump should not be installed too deep. The intention is to intercept shallow water and allow dispersal in normal conditions, not to create a system that is permanently lowering the groundwater level. Water below ground is natural and usually doing no harm. In most locations it would be unusual for groundwater to sit higher than the 0.635 m depth of the Iguazu 635 chamber for long periods, so using a deeper perforated chamber would risk unnecessary continuous pumping. The appropriate depth will always depend on the ground conditions and local water levels.
Another method is to use the sump as a high-level overflow on an existing drainage system. When the gravity outlet stops working (for instance if a non-return valve closes) the flow diverts into the chamber and the pump activates. We have a case study showing exactly that which you can read here: Case Study: Sump Pump Installation to Manage Floodwater at a Riverside Property
A sump pump is just a pump in a chamber, but there are a lot of ways they can be used. As well as flood management they allows surface water and foul drainage to be lifted from areas where gravity drainage is not viable.
To avoid common sump pump mistakes read more here: Avoiding Common Sump Pump Mistakes (We See These a Lot)
What started as a routine pump enquiry became a bespoke engineering review. This real project shows the difference between buying a pump and designing a pumping system – and why that distinction protects performance, reliability and long-term cost.
A sump pump is an automatic water pump installed in a chamber at the lowest point of a property to collect and remove water when levels rise. Used for flood control, basements, garages and pumped drainage where gravity outfall is not possible, a correctly sized and installed system becomes a reliable, low-intervention water management solution.
The best automatic basement pump isn’t necessarily the biggest – it’s the one that works with how the property actually floods. This guide explains the causes, the pump options and the installation details that make the difference between moving water and keeping a cellar dry.
