Further to our 22 May 2026 article, Top 5 Puddle Pumps for Flood and Dewatering, where we ranked the best puddle pumps we stock, this guide picks up where that left off. The focus here is automatic low-level pumping: how to clear water from a floor on its own, with nobody present.
Standing water on a floor is one of the most awkward problems to drain. Ordinary submersible pumps stop working once the water gets shallow. In a basement, lift shaft or plant room that floods while nobody is there, that residual water can sit for hours or days before anyone notices.
The good news is that low-level water can now be removed automatically, far lower than a conventional automatic pump manages, with no one present and no control panel on the wall. This guide explains how automatic floor-level pumping works, why most "automatic" pumps cannot get close to the floor, and which pump to choose.
Why Most Automatic Pumps Leave Water Behind
Most automatic pumps switch on and off using a float switch. A float is a buoyant device on a cable or guide that lifts as the water rises and drops as it falls, flicking a switch to start or stop the pump.
The problem is simple physics. A float needs a useful depth of water to rise and fall. At floor level there is not enough water to lift it, so the float stops the pump early and leaves a layer of water behind. You can see this on the pumps themselves: a popular dual-mode puddle pump like the EGO 500 Gi will pump down to around 10mm under manual control, but only to around 60mm once it is left to run automatically on its float. That difference is the float switch, not the pump.
To pump automatically much closer to the floor, you need a level control that does not rely on depth at all.
How Automatic Floor-Level Pumping Works
The answer is a floor-level sensor. On our automatic Residox puddle pumps this is a probe called the Crab. Instead of floating, it rests flat and weighted on the ground and detects the presence of water by sensing the surface it is sitting on.
Here is what makes it suited to low-level work:
- It sits on the floor, so it works at floor level. There is no float to lift, which is why it keeps the pump running at water levels far lower than a float switch can reach.
- It comes ready wired to the pump. The sensor is supplied already connected, so there is no control panel to mount and no wiring to do. You plug in and go.
- The timing is adjustable. Using a magnetic key, you can set how long the pump waits before it starts once water is detected, and how long it keeps running after the water clears. From the factory the pump starts a few seconds after water is sensed and stops around half a minute after the floor is clear, which prevents the pump short-cycling on and off.
- It copes with clear or flood water. That suits real flood and drainage water rather than just clean water.
The result is genuine set-and-forget protection. Water arrives, the pump runs, the floor is cleared to near-dry, and the pump shuts itself off until next time.
The Pump: EVAK Residox 400 and 750 Automatic
The floor-level sensor is paired with the EVAK Residox, one of the most capable low-level pumps available. The automatic version comes in two outputs:
- EVAK Residox 400 Automatic, with a 250 litres per minute flow rate and an 11 metre head, for most domestic and commercial floor-drainage jobs.
- EVAK Residox 750 Automatic, our highest-flow puddle pump at 330 litres per minute and a 16 metre head, for larger areas, longer hose runs or discharge uphill.
Both automatic models are 230V only, which suits domestic and general-purpose mains installations. If you need a 110V option for site use through a transformer, that is available on the manual Residox rather than the automatic version.
Across the range the build is the same: a stainless steel outer case and handle, a cast iron pump housing, an abrasion-resistant Hytrel vortex impeller, and a rubberised NBR base that is surface-safe on tiles and finished concrete. No priming is required. You place it in the water, and the sensor does the rest. You can see both automatic models on our Puddle Pumps collection.
Where Automatic Floor-Level Pumping Is Used
This setup is ideal anywhere water can appear when no one is watching:
- Basements and cellars prone to groundwater or storm ingress
- Lift shafts where water collects at the very bottom
- Plant rooms and pump rooms that must stay dry to protect equipment
- Unattended commercial units, garages and stores that flood overnight or at weekends
- Hard-to-reach low points where sending someone to run a pump manually is impractical
- Flood control and behind flood barriers to reduce damage, and provide "passive" pumping for less stress.
In each case the benefit is the same: passive, unattended flood defence that clears the floor far better than a float-operated pump, in the defined areas where water periodically collects.
Manual or Automatic: Which Do You Need?
Both have their place.
Choose manual if you want the lowest possible finish and full operator control, and you will be present during pumping. A manual Residox under direct control will clear water down to roughly 1mm, which is why it is the choice for attended flood response, temporary jobs and hire fleets, and it is also where the 110V site option lives. For a real-world example, see how the manual EVAK Residox was used to clear seepage on our blog Using an EVAK Residox Puddle Pump Behind a Flood Barrier.
Choose automatic if the pump needs to look after itself in a space that is not constantly supervised. The floor-level sensor turns the Residox into permanent passive protection that reaches far lower than a float-operated automatic, which is what most basement, lift shaft and facilities applications actually need.
Frequently Asked Questions
Can a puddle pump really be automatic?
Yes. With a floor-level sensor rather than a float switch, a puddle pump can start and stop on its own while still clearing water far closer to the floor than a standard automatic pump.
Why will a float switch not work well for low-level pumping?
A float needs enough depth of water to rise and fall. At floor level there is not enough water to lift it, so it triggers off early and leaves a layer behind. A floor-resting sensor avoids this because it does not rely on depth.
How low will it pump?
The Residox pump clears water down to around 1mm under manual control. In automatic mode the floor-level sensor holds the pump on far lower than a float switch manages, getting close to the floor, though for the absolute lowest finish a manual pump under direct control still has the edge.
Do I need a control panel?
No. The floor-level sensor comes already wired to the pump, so there is no control panel to mount and nothing to wire in. The automatic Residox arrives ready to use.
Is the automatic version available in 110V?
No. The EVAK Residox 400 and 750 Automatic are 230V only. If you need 110V for site use, choose a manual Residox with a transformer.
Can it handle dirty water?
Yes. The sensor works in clear and dirty water, and the Residox uses an abrasion-resistant Hytrel vortex impeller built for real drainage and flood water.
