Bilge Pump for Your Boat: How to Choose the Right One (Freshwater)

A bilge pump (also called a sump pump in Dutch) removes the bilge water that collects in the bottom of the hull: rain, condensation, splash water, and leaks. For freshwater on board where 230 volts are 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 automatically. For salt or brackish water, choose a corrosion-resistant version.

Bilge pump or sump pump: what's the difference?

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

Why the Simer 6S as a bilge pump?

The Simer 6S is specifically suitable as a sump or bilge pump for freshwater on board. It sucks flat down to 2 mm, so hardly any water remains in the bilge — no standing water, no odor, and no extra weight in the hull. With 6,000 liters per hour and up to 6.5 m head, it quickly pumps the bilge water out.

Built-in level switch: automatic on and off

The big advantage of the 6S is the built-in level switch. It automatically activates the pump from approximately 7 mm of water and switches off again when the bilge is dry — without a separate float. Ideal for a boat you don't check daily: the 6S keeps the hull dry independently.

Freshwater or saltwater? The material decides

The Simer 6S has an aluminum motor housing with a plastic pump housing and is therefore made for freshwater (inland navigation, lakes, houseboats). In salt or brackish water, corrosion quickly affects aluminum and cast iron; choose a fully stainless steel (RVS) submersible pump here. Is stainless steel too expensive? Then a fully plastic submersible pump is a more economical alternative that is just as resistant to salt, because plastic does not corrode — provided both the pump housing and impeller are made of plastic.

What to look for in a bilge pump?

• Flat suction capacity: the 6S removes water down to 2 mm, leaving the bilge almost dry.
• Automatic switching: the built-in level switch activates from approximately 7 mm — useful for unsupervised use.
• Voltage: the 6S operates on 230 volts (shore power or on-board power). If your boat only has 12/24 volt DC, a special DC bilge pump is needed.
• Material: freshwater with the 6S (aluminum/plastic); salt or brackish water with stainless steel or a fully plastic pump.
• Flow rate and head: 6,000 l/h up to 6.5 m — more than enough to discharge bilge water to the deck or transom.

Common mistakes

• Using an aluminum 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 beforehand.
• Choosing a flat suction pump without automatic switching for a boat that is left unattended for a long time — the 6S switches itself.
• Accepting too much residual water. A regular pump leaves inches; the flat-suction 6S goes down to 2 mm.

Our recommendation

For freshwater 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 are in salt or brackish water, choose a stainless steel or fully plastic pump. In doubt? View our range of submersible pumps or contact our customer service.

Frequently Asked Questions

What is a bilge pump?
A bilge or sump pump removes the bilge water that collects in the bottom of the hull, such as rain, condensation, and leaks.

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

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

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