The latest potable water pumps for narrow boats are based on a DC powered motor which drives multiple diaphragms in the head of the pump.

How many diaphragms depends on the specification of the pump, with the standard commonly sold units having 3 and the top end products having 4. These compact pumps have smooth flow characteristics, are self priming and, depending upon the model you’ve specified, can service multiple outlets at once.

These pumps, common to all major manufacturers, are supplied with snap-in ports for both barbed hose connectors for 13mm (½ inch) pipework and easy install push fit pipe connectors.

The common leisure pump for a narrowboat will produce a flow rate of around 11 litres per minute and draw around 4 to 5 amps maximum.

How They Work

It’s very simple really. The pump is wired into a DC power supply. An electrical pressure switch in the pump is set to close or open at a certain PSI or pounds per square inch.

When a tap on a narrow boat is opened the switch detects a pressure drop in the pipework and allows the pump to run. When the tap is closed, the pump runs for a few seconds to allow pressure to build up to a pre-set level in the pipework, at which the pressure switch turns the pump off.

It’s important to know the pressure parameters of your pump if you are to effectively use an accumulator tank.

Knowing that a pressure switch is fitted can help you to diagnose a problem in your water system.

If all the taps are closed and there are no drips from taps but the pump runs intermittently, say after a few hours of inactivity in the middle of the night, then you have a leak.

The leak may be the seals on the head of the pump itself, they do go after a few years. This is easy to check as it will be wet around the pump body. However, if all is dry at the pump and the taps are not leaking then water must be being lost at a joint somewhere.

Have a look in you access hatch in the cabin floor at the rear of your boat to see if there is evidence of water.

If you have no access hatch, you will just have to follow the runs of pipework until you find the leak. Make a note to get an access hatch cut!

Turn the pump off at the main fuse board if you are leaving the boat for a couple of days or more. Open a tap and relieve the pressure in the system. It’s kinder on seals and joints this way and it doesn’t take long for a pump to empty a water tank in the bilge if a leak occurs!

Installation requires reference to the manufacturers instructions but we can give you a general overview here.

Very occasionally you may run completely out of water. Despite having run-dry protection so as to not burn out the motor, it is standard practise to install the pump as close to the water tank as possible. This ensures that as it primes itself, seals are not damaged through over heating due to lack of lubrication. Mesh filter assemblies which connect directly to the inlet port of the pump are often a requirement of the warranty from the manufacturer. Fit one in any case as they will protect your expensive pump from damage from any large foreign objects that may have fallen into the tank. They are £5 well spent.

The pump should be mounted to a solid surface to minimise vibration.

Ensure any DC cable that you run to the pump is sized for suitability and voltage drop.

Proven marine water pumps are readily available from all good chandlers ready to be fitted to your narrow boat.

Narrow boats waste water from sinks that are higher than the water line through pipework that is directly connected to through hull fittings.

Washing machines have their own built in pumps. Therefore for fittings that waste below the water line such as baths and shower outlets, we have to give the so called grey water a helping hand.

Problems associated with pumping water upwards are related to gravity and weight of water. Therefore we need to specify a pump that can cope with the “vertical lift”. Fortunately there are some very good units, available from all good chandleries and on-line that are proven in service. Because these pumps clear water from waste pipes, they suck air on the last few cycles and are designed to run “dry”.

Heavy duty motors are designed for long life and the internal construction means they can cope with the mixture of hair and soap that wastes from showers and baths. Installation should be referenced to the manufacturers instructions, with an eye on warranty, wiring and plumbing connections.

Ensure you have good access on your narrow boat for future inspection or removal and that the pump has a good air supply to prevent overheating.

Two types of waste water pumps are commonly available:

• In-line diaphragm pump

The conventional pump has to be turned on and off manually. The sump pump is activated by a float in a box that rises as water flows into the box. Therefore operation is automatic.

• Sump Pump

The flip side to this system is that there are more moving parts to  potentially go wrong. If the float sticks… Therefore regularly inspect the sump box and remove any obstructions or build ups of hair.

Final Note:
Finally, we are aware of some narrow boats that are built with waste water draining straight into the cabin bilge. The evacuation of this waste is done by a bilge pump. If you have this system, consider removing it and moving to a direct pump through the hull. Constant water in the cabin bilge will eventually rot the base plate and is unhealthy.

The bilge is the lowest area within the narrow boat. Basically the whole area directly above the base plate from bow to stern, below sub floors and engine. Reference is usually given only to the area directly underneath the propeller shaft in the stern, but it is important to remember the cabin bilge.

Bilge pumps should be fitted where ever this area is divided by a solid bulkhead. The collection of water in the cabin bilge can come from condensation, leaking water pipes, or even leaking windows.

We know of owners who had no idea of water collecting in their cabin bilge until the narrowboat was hauled out on an angled slipway and water rushed out from the bases of cupboards!

Narrow boats are designed so that any water that gets into the cabin bilge can drain down towards the rear. Some have an open bilge that runs straight into the engine bay. Others have a wooden, now usually steel, bulkhead that separates the cabin bilge from the engine bilge. It is in this case and against this bulkhead you should install a bilge pump.

There are various types available from the usual suspects. Some require a manual switch to operate, others are fully automatic. Installation follows the manufacturers guidance, but again, if you are unsure follow our advice for cable specification. Pay particular attention to the rating of the outside cable insulation as bilges are harsh places.

If the pump is automatic, i.e it uses a float to activate the motor, then wire it so that it is always on. There is no point in having an automatic pump that doesn’t work when you’re not there if required.

Incidentally, bypassing of battery isolation switches by bilge pump installations is one of the few allowable exceptions of the Boat Safety Scheme. Your examiner will check so do it in accordance with the BSS.

The same applies to bilge pumps in the engine room, which as we mentioned earlier are usually sited in a bund area under the propeller shaft.