top of page

Rainwater harvesting underground

Rainfall is expected to become more common and more intense, followed by a prolonged drought with a ban on irrigation, etc. We are not used to this and it is noticeable not least in urban environments with congested and undersized water supply networks with floods as a result (during the heaviest rainy periods). Expanding only the water and sewerage networks is a bit like turning a blind eye to the cause itself and only doing something about some of the consequences. We need to do more and, above all, think more preventively!

Today we are used to:

  • Go to the toilet to meet our needs and then flush the toilets with clean drinking water ...

  • Clean our homes with clean drinking water ...

  • Wash our clothes in clean drinking water ...

  • Water the gardens and flowers with clean drinking water ...

We could have done all this with clean and filtered rainwater!

In fact, we can even save money on doing so if we comparatively use municipal water, then we have both water and the sewage tariff to deduct from. The cost of municipal water and sewage will not decrease but is expected to increase every year. So it is not only the environment we save on but also on future expenses!

Each person is expected to use huge amounts of drinking water completely unnecessarily, as anaverage we consume the following amounts:

  • Flushes about 13 500 liters of water in the toilet per person / year.

  • Cleans our homes with about 2,500 liters of water per person / year.

  • Washes clothes with about 5,500 liters of water per person / year.

  • We water our gardens on average with 150-200 liters / m2 of garden area.

By only using the rainwater from our house and garage roofs, we can often recoup the investment financially in just a few years. Of course, if you build a new house, it goes much faster!

A standard household saves about 50% of drinking-water and a company saves about 70-85%!

Thanks to our collaboration with Graf, we can now offer complete solutions to easily take care of the rainwater.

Fully automated tank and pump systems with self-cleaning filters make the whole thing basically maintenance-free.

This is how it works:


  1. A tank is buried underground, or placed in the basement if there is room for this. (at larger sites, you can also use the EcoBloc series to customize your project.

  2. The rainwater from the rooftops is led down to the tank through a self-cleaning and easily accessible filter.

  3. A separate pump unit is installed inside the house which is connected with two pipes to the tank. One pipe with drinking water to the tank and one with rainwater from the tank. The line with drinking water to the tank is only used to flush the filter.

  4. A pipeline is connected from the tank to an infiltration system, stormwater system or both and, through this pipe, excess water is led in case the tank becomes full.

  5. Inside the house, pipes are drawn to water ejectors for watering the garden, toilets, washing machine and water tap for cleaning water.

How advanced installation you choose to do is of course up to everyone. Some choose to only connect water ejectors, washing machines and a cleaning sink. Some choose to go all the way and connect water ejectors, washing machines, cleaning sinks, toilets and perhaps even supplement with an extra free-standing water ejector close to a greenhose etc.

There are several different sizes of tanks and many parameters to take into account to calculate the optimal volume, if you choose a too small tank, it will consume unnecessarily amount of drinking water and the savings will not be as great. if you choose an unnecessarily large tank, the installation can become unnecessarily expensive.

If there is room in the basement of the house, it is easy to supplement with more tanks if you subsequently want to supplement your installation with, for example, another toilet.

Which system best suits your project and how big the savings will be depends on a number of different factors:

  1. Number of people in the household.

  2. The ground cover area / areas of the roof / rooftops

  3. Average rainfall per year.

  4. The price you pay today for water and sewage.

  5. For what you intend to use the water.

  6. How many days of water buffer you want.


Does that sound complicated? Do not worry! Of course we help you all the way!

If you want to check on your own, there is a very good tool on graph's website: Click here to get to the product advisor.

If you have already looked at the product selector and downloaded a proposal, you are welcome to email the downloaded proposal to us and we will help you with a quotation.

It is not only private individuals who can benefit from the rainwater. Many industries can make the same savings and many times even bigger savings! Think of all the staff who use the toilets, the large floors that have to be scrubbed with scrubbers, work clothes that have to be washed, cooling water for many machines and the often very large ceilings that can be used to collect water!

A smart way of thinking to ensure a sustainable future – we call it Eco-Logic!


Hercules tanks

The benefits of Hercules tanks are many.

  • They are transported in each other and built together on site, which means that the transport cost is low while CO2 emissions are lower.

  • They can be installed in the basement of the house if there is room for this. It is also possible to supplement with more tanks as you connect more toilets etc.

  • A Hercules tank is quickly assembled from two halves in place without special tools, a hammer and a spacer to knock the locking wedges in place are all that is required.

  • One tank half fits through a standard door (≥ 80 cm).

  • The Hercules tanks can be dug into the ground with the groundwater level up to the top of the tanks, with at least an 80 cm ground earth corvering.

  • A Hercules tank can also be used for rainwater harvesting above ground as a very affordable alternative.

Li-Lo Tanks

The advantages of Li-Lo tanks are that they can be buried very shallow thanks to their "flat" shape and their construction in three layers that provides an insulating effect. However, we recommend that the tank is always dug down to a frost-free depth.

bottom of page