How to choose a rainwater pump

Have you decided to use rainwater and collect it in a retention tank or other collection point? Now you need to decide which pump to choose to meet your requirements.

Rainwater pumps mostly fall into the category of wastewater pumps, as they are most often pumping slightly polluted water containing small impurities. However, you can also use surface pumps with the necessary accessories that are located outside the tank. The most comprehensive solution is the range of rainwater pumping stations. 

Wastewater pumps

You can use pumps that can handle dirt up to a maximum size of 10 mm. For types with a suction basket at the bottom, a safety gap between the suction basket and the bottom of the tank, which usually contains a variety of sediment (at least 30 cm), must be taken into account. Some variants are equipped with a "side suction" to which a suction hose with a floating filter is connected. This  ensures that the best quality water supplied in the tank (approx. 10 cm below the surface), and also allows the pump to be placed at the bottom, thus making better use of the reservoir. The pump should have a sufficient delivery pressure, minimum of 20m water column (usual wastewater pumps have a delivery pressure of approx. 8 m, which is insufficient for an irrigation sprinkler hose, for example). Types with an integrated float protection to prevent the pump from dry-running, or types constructed for partial submersion are better choice. 

Surface pumps

These are simpler in design and therefore usually cheaper. However, their use has several limitations. First of all, there is a suction pipe, the total resistance of which must not exceed (depending on the pump type) 6 m in most cases. Furthermore, a certain noise level must be taken into account. The suction should be supplied with a floating suction basket with a swing check valve to ensure pumping of the best quality water in the tank (about 10 cm below the surface).

Rainwater pumping station

These are devices offered by renowned pump manufacturers and directly adapted to rainwater harvesting technology. They are equipped not only with suitable pumps, but also with differently sized safety tanks (they do not replace rainwater tanks but allow an efficient connection to the water supply network in case of drought) and control automation including operation protection.
It is therefore up to you which method you prefer and what your options are in terms of pump location.

First, you need to determine the pump usage.
If I want to use the water in the tank for irrigating the garden or if I want to connect it to the house and use the water for flushing the toilet, for example, the choice of pump and then especially the accessories will vary considerably.
This decision also affects, for example, the amount of subsidies that can be obtained from government support programmes. While strict design requirements must be observed when using rainwater for flushing as well, the savings and support are greater.

The pump connected to the interior applications also needs to be supplied with necessary accessories such as filtration systems or fittings for recharging water in times of drought to ensure that the system is always functional and does not get damaged.
The next step is to decide the required pump flow rate, the delivery height and the desired final pressure.

This depends on your local conditions.

The required pressure is an important parameter. When watering your garden, you don't want to deal with a weak water outlet insufficient for irrigating your garden bed (the pressure at the outlet of the system/hose should be at least 0.1 MPa)

  • How far the tank is from the water intake point,
  • what is the ground elevation there
  • What is the diameter and how long is the pipe through which the water will flow.

The required flow rate is then determined by the anticipated use of the rainwater.

  • Number of toilets or washing machines connected
  • The size of the area to be irrigated
  • Irrigation technology (for automatic irrigation, the required pressure and minimum flow rate must be determined - values provided by the irrigation contractor)

Submersible automatic pump

This is probably the best solution for most common applications when pumping water from a retention tank. The submersible pump is located directly in the tank and its automatic control ensures smooth operation without the need for on/off switching. At the same time, the pump is supplied with a float switch so in the case of insufficient water level, the pump will automatically switch off and protect the pump against damage.

The submersible pump is not the only solution. You can also use a surface pump that is placed outside next to the tank. It's up to you which method you prefer and what your options are in terms of pump location.
Monitoring the water level in the tank

If you don’t choose an automatic pump, with various integrated functions, you need to solve the issue of level monitoring. 
There are various probes and assemblies for tank filling. You definitely need to get some for the tank to ensure smooth operation of your pump. This will keep you aware of how much water is in the tank and prevent any problems with the pump running dry.

Submersible pump sets - the complete solution

If you are overwhelmed by the choice of tank, pump and all of the accessories, we have prepared ready-made kits that contain everything you need for the installation. 
It is then necessary to check that the size of the tank matches your needs, as well as the technical parameters of the pump. We have already checked the compatibility between the individual components for you.


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