How does the water get into the tank?

Reading time 3 minutes

Updated - October 13, 2024

How does the water get into the tank, e.g. from the pond, lake or well? There is enough pressure at the tap to penetrate filter stages and have clean water in the tank.

However, if there is a lack of pressurized water from the tap, you have to generate pressure yourself if you also want to filter the water to be filled in, which will be the case 99.9 % of the time, especially in the great outdoors.

A 12V DC pump, a floating ball with filter basket, a 1″ suction hose with pressure hose and cable to supply the pump provide a remedy.

The choice of pump

At home, the first thing that comes to mind is the submersible pump, which is self-priming, pumps a lot of water in a unit of time and usually even has a decent water pressure on the outlet side. But: it only works with 230 V AC. And not everyone has enough battery capacity to provide around 1 kW via an inverter.

That leaves the 12 V pump. Shurflo is probably the best-known manufacturer in the marine and motorhome sector.

The currently most powerful 12 V pump suitable for continuous operation is the Shurflo diaphragm pump type 2088-713-515. With an open outlet and level pipe routing, the maximum delivery rate is 13.2 liters / minute. It offers a delivery pressure of 4.1 bar and a suction height of up to 3 meters.

Taking into account pressure losses through hoses, couplings and delivery head to the water filler neck of the motorhome, you will ultimately end up with around 8 ... 10 liters / minute. This would fill a 150 liter water tank in 15 ... 20 minutes, which corresponds roughly to the speed of a conventional domestic water tap.

The suction strainer with floating ball

To extract water from a body of water, you could simply use a conventional suction hose with a filter basket and non-return valve. However, this would come to rest in the mud and cause a lot of sand to accumulate.

Consequently, the suction basket should float freely above the ground in order to suck in as little solid matter as possible. This is why there are so-called SAFF (floating suction fine filters), which, thanks to the floating ball and the weight of the filter and the suction hose connected to it, keep the filter free from the substrate.

As all Shurflo pumps have a 1″ external thread for connecting the suction and discharge hoses, the only remaining option is the corresponding SAFF with 1″ connection as well with built-in non-return valve.

The suction hose should be around 4 ... 5 m in length so that you can get far enough away from the shore and also so that you don't need too much weight and space to store it.

The connection cable

At 2.4 bar, the pump has a flow rate of just under 9 liters / minute and requires around 10.2 A for this. Mathematically, with a cable length of 15 m, this corresponds to a required cable cross-section of 22.7 mm²rounded up to 25 mm².

As you do not want to roll out two separate cables for plus and minus, but ideally prefer a double cable, this is available as a Twinflex - Highly flexible twin cable 2 x 25 mm² e.g. here to obtain.

Why such a long cable? Because you can rarely drive so close to the water that you can safely stand directly on the bank without sinking in. Of course, the pressure hose must also be long enough.

The cable can be connected on the on-board side using a cable connector available as a set. HISports 120 A Plug and (built-in) sockets manufacture. The contact pins are intended for crimping, but as the cable cross-section is smaller, soldering (with a soldering lamp, as a soldering iron is not powerful enough) must be used.
The 25 mm² The cable is first roughly tinned, inserted into the sleeve and the gap filled with tin.
The pump connection cables are covered with heat-shrink tubing (self-adhesive) and soldered directly to the pump connection cables.

Filter unit

A PP and a stainless steel filter serve as pre-filters, which are attached to the support plate of the housing by means of a double filter housing. The filter inlet connection is made using a feed-through fitting with a screwed-in suction connection, decoupled via rubber seals.

The filter outlet leads via a suction hose to the inlet of the diaphragm pump, whose pressure outlet, again decoupled from vibration via the hose section, leads to a wall bushing with a ½" female thread, via which either a hose nozzle or a Gardena hose connection can be adapted,

End product

The above components can be combined in a suitable Housing can be installed. For easy portability, the following are suitable Bow handles quite well. Protect against damage to the base of the housing Solid Rubber buffer with M10 thread.

Left - Connection terminals for the power supply to the pump
Center - Two pre-filters connected to the diaphragm pump by means of a suction hose
Right - suction hose at the top - pressure hose connection at the bottom