Quick answer: For a flooded lawn, patio or path, where the water is only a few centimetres deep, choose a puddle pump. A typical dirty water pump with a float switch needs several centimetres of water to start and stops with water still standing, while a puddle pump clears down to 1 to 2mm. Choose a dirty water pump when the water is deep and carries leaves, grit or larger debris, such as a sump, pond, pit or flooded cellar.
When customers call us about a flooded garden, many have already been told to buy a “dirty water pump”. It’s the answer you’ll often get from a search engine or an AI assistant, and it isn’t wrong exactly. Dirty water pumps are tough, handle debris and move a lot of water. The problem is what they leave behind.
The difference in one sentence
A dirty water pump is built for depth and debris. A puddle pump is built for shallow water.
Garden flooding is often shallow: a few centimetres across a lawn, a patio or a path. That’s exactly where the two types part company.
Why dirty water pumps leave water behind
Most dirty water pumps draw water in through a strainer around the base and need to be covered with water to keep running. When the water gets too shallow, they lose suction and stop, typically leaving 50mm or more standing.
Automatic versions add a float switch, which needs depth to rise and switch the pump on. As an example from our own range, the automatic version of the Mizar stainless steel submersible pump switches on at around 220mm and off at around 90mm. That’s perfect in a sump. On a patio with 40mm of water, it would never start.
A puddle pump draws water from right at floor level:
- The Stream SPP2-4 clears down to about 2mm.
- The Stream SPK530 and Tsurumi LSC1.4S clear down to about 1mm.
- Automatic puddle pumps use low-level sensors instead of floats. The Stream SPP2-4A starts at about 20mm, and the EVAK Residox 400 Automatic detects water at about 3mm.
The result is a patio that’s damp rather than under water. More on how they work in what is a puddle pump?
Side by side
| Typical dirty water pump | Puddle pump | |
|---|---|---|
| Best for | Deep water with debris: sumps, ponds, pits, cellars | Shallow water on flat surfaces: lawns, patios, paths, garages |
| Water left behind | Often 50mm or more | About 1 to 3mm |
| Automatic switching | Float switch, needs depth to rise | Low-level sensor, starts at a few millimetres or centimetres |
| Solids | Large: often 20 to 35mm | Small: usually a few millimetres |
| Flow | Often higher | Lower, but works where the water actually is |
What about litres per hour?
You’ll often see dirty water pumps sold on big flow figures, such as 10,000 to 20,000 litres per hour. Two things to bear in mind:
- That’s the maximum, at zero lift and no hose. Once the pump has to push water up a slope and along a hose, the real flow is much lower. See why max flow is not your real pump flow.
- Flow only matters while the pump is working. A high-flow pump that stops at 50mm moves nothing once the water drops below that.
To compare like with like, here are some of our puddle pumps in litres per hour (maximum):
- Stream SPP2-4: 70 L/min, about 4,200 L/h
- Stream SPK530 and Tsurumi LSC1.4S: 170 L/min, about 10,200 L/h
- EVAK Residox 400: 205 L/min, about 12,300 L/h
- EVAK Residox 750: 330 L/min, about 19,800 L/h
Which should you choose?
Choose a puddle pump if:
- the water sits a few centimetres deep on a lawn, patio, path or drive;
- you want the surface as close to dry as possible;
- the water is rain or run-off with only light grit.
Choose a heavy-duty puddle pump if the garden floods most winters or the area is large.
Choose an automatic puddle pump if water arrives while nobody is home.
Choose a dirty water pump if the water is deep and carries leaves, grit or small stones: emptying a sump or soakaway chamber, a flooded cellar, a pond or a pit. The BBC Semisom 262 passes solids up to 32mm and moves up to 425 litres per minute. See pump solids handling explained for what free passage means.
Got both? Many customers do. A dirty water pump takes down the deep water fast, then a puddle pump finishes the job.
Where should the water go?
Before you start, make sure the water has somewhere sensible to go: a surface water drain, gully or soakaway that falls away from your house and your neighbours. Don’t pump into the foul sewer, and check before discharging to a ditch, stream or river, as permission may be needed. Floodwater can be contaminated, so wear gloves and keep children and pets away. Our guide to a flooded garden covers the first steps in more detail.
Order online, or by phone. Order by 2pm for next working day dispatch.
