Bilge pump for your boat: how to choose the right one (fresh water)

A bilge pump (called a "lenspomp" in Dutch) removes the bilge water that collects at the bottom of the hull: rain, condensation, spray and leakage water. For fresh water on board where 230 volts is available, the Pentair Simer 6S is the ideal choice: a flat suction submersible pump with a built-in level switch that pumps down to 2 mm and starts by itself. For salt or brackish water, choose a corrosion-resistant version.

Bilge pump or "lenspomp": what is the difference?

There is no difference: bilge is the English term for the lowest part of the hull, lens the Dutch one. A bilge pump keeps that space dry. On larger vessels it is permanently installed; on smaller freshwater craft and houseboats you often use a portable or semi-permanent submersible pump.

Why the Simer 6S as a bilge pump?

The Simer 6S is particularly well suited as a bilge pump for fresh water on board. It pumps flat down to 2 mm, so hardly any water remains in the bilge — no standing water, no odour and no extra weight in the hull. With 6,000 litres per hour and up to 6.5 m of head, it moves the bilge water overboard quickly.

Built-in level switch: on and off by itself

The big advantage of the 6S is the built-in level switch. It activates the pump automatically from about 7 mm of water and switches it off again once the bilge is dry — without a separate float switch. Ideal for a boat you do not check every day: the 6S keeps the hull dry on its own.

Fresh water or salt water? The material decides

The Simer 6S has an aluminium motor housing with a plastic pump housing, which makes it designed for fresh water (inland waterways, lakes, houseboats). In salt or brackish water, corrosion quickly attacks aluminium and cast iron; there you should choose a fully stainless steel submersible pump. Is stainless steel too expensive? Then a fully plastic submersible pump is a more affordable alternative that handles salt just as well, because plastic does not corrode — provided both the pump housing and the impeller are made of plastic.

What should you look for in a bilge pump?

• Flat suction capability: the 6S removes water down to 2 mm, so the bilge stays almost dry.
• Automatic switching: the built-in level switch kicks in from about 7 mm — handy for unattended use.
• Voltage: the 6S runs on 230 volts (shore power or on-board mains). If your boat only has 12/24 volt DC, you need a dedicated DC bilge pump.
• Material: fresh water with the 6S (aluminium/plastic); salt or brackish water with stainless steel or a fully plastic pump.
• Flow rate and head: 6,000 l/h at up to 6.5 m — more than enough to discharge bilge water to the deck or transom.

Common mistakes

• Using an aluminium pump in salt water. Choose stainless steel or fully plastic instead.
• Trying to run a 230V pump without 230V on board. Check your on-board power supply beforehand.
• Choosing a flat suction pump without automatic switching for a boat that is left unattended for long periods — the 6S switches itself.
• Accepting too much residual water. A standard pump leaves centimetres behind; the flat suction 6S goes down to 2 mm.

Our recommendation

For fresh water on board with a 230V connection, the Pentair Simer 6S is the complete solution: flat suction down to 2 mm and fully automatic thanks to the built-in level switch. If you moor or sail in salt or brackish water, choose a stainless steel or fully plastic pump. Not sure? Browse our range of submersible pumps or contact our customer service.

Frequently asked questions

What is a bilge pump?
A bilge pump removes the bilge water that collects at the bottom of the hull, such as rain, condensation and leakage water.

Which bilge pump for fresh water?
The Pentair Simer 6S: a flat suction pump with a built-in level switch that pumps down to 2 mm and switches on automatically from about 7 mm (230V).

Does the Simer 6S switch on automatically?
Yes, the 6S has a built-in level switch that kicks in from about 7 mm of water and switches off again once the bilge is dry — no separate float switch needed.

What if stainless steel is too expensive for salt water?
A fully plastic submersible pump is a good, more affordable alternative: plastic does not corrode. Make sure both the pump housing and the impeller are made of plastic.