The term “sub pump” is fundamentally short for Submersible Pump, meaning a submersible water pump. The term though is mostly used as a slang term in construction sites.
Ask ten people on a building site for a “sub pump” and you may get ten slightly different interpretations. That’s where confusion often starts.
In most cases, when someone refers to a sub pump, they are talking about a submersible pump used for site drainage or dewatering. That could be anything from clearing flooded foundations, draining trenches, pumping groundwater, through to keeping an excavation dry after heavy rain.
Sub pumps may also form part of a permanent system, such as a packaged pump station. These are often used where gravity drainage isn’t possible, including foul water systems or surface water management, or as part of a negative waterproofing strategy using cavity drainage membranes.
The challenge with the term is that it isn’t specific.
A request for a sub pump to “drain a site” could mean very different requirements depending on the conditions:
Draining foundations or trenches may require a heavy-duty site pump with an agitator, such as an EVAK Trenchman, where the agitator is designed to keep solids in suspension for more efficient pumping. By contrast, draining water from a finished slab may be better suited to a Puddle Pump, which can pump down to just a few millimetres.
A puddle pump is still a submersible pump, just a very specific type designed for low-level water removal.
When people talk about sub pumps in construction, they are usually referring to contractor-grade site drainage pumps. Some of the most widely used examples include:
The Tsurumi LB series are tough, single-phase submersible pumps designed for harsh site conditions, offering reliable performance, long service life, and low maintenance. They are widely used across construction, utilities, and flood defence.
Designed specifically for trench and foundation dewatering, the EVAK Trenchman includes a built-in sintered agitator that keeps solids moving. This makes it particularly effective in excavations where silt and fines would quickly block a standard pump.
The EVAK Drainox range is a robust site drainage pump built for demanding environments. It’s a straightforward, durable choice for contractors who need dependable performance in dirty water conditions.
On UK construction sites, 110V submersible pumps are the norm. The reduced voltage significantly lowers the risk of electric shock in wet and hazardous environments. Power is supplied via an isolating transformer with a centre-tapped earth, aligned with HSE guidance.
While 230V pumps exist, they are typically more appropriate for permanent installations or controlled environments rather than active construction sites.
Site Drainage Pumps are built to do things standard submersible pumps are not.
They are designed to handle dirty water, solids, high flow rates, and continuous use in rough conditions. As a general rule, they have tough casings, abrasion-resistant impellers, and overall heavier more durable construction. Domestic or light-duty submersible pumps simply won’t survive long in these environments.
You can view our full range of site drainage pumps here:
If you’re being asked for a “sub pump”, the right first step is always the same: clarify what water you’re pumping, from where, to where, and under what conditions. The pump choice follows from that.
What is a packaged pump station and when are they used? This article explains how pump systems can form part of a wider flood resilience strategy, using a real Flood Risk Assessment example from a property in Flood Zone 3.
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.
