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Gray water recycling system in the Botanica apartment building Foto: Skanska Reality a.s.

Gray water recycling system in the Botanica apartment building

At first glance, the Botanica K apartment building in Jinonice, Prague, is not very different from the surrounding houses in this residential area. The difference is how it handles drinking water.

In most Czech households the so-called gray water - water from showers, washbasins and bathtubs, drains into the sewerage system without any further use. The technology used by Skanska in this house allows the reuse of gray water, especially for flushing toilets, or even watering plants. Thanks to this, it is possible to save up to 26 % of usual drinking water consumption.

Moreover, the project is not only exceptional for the gray water treatment technology. It was the first in the Czech Republic to receive the BREEAM Excellent international environmental certification which assesses the building from the point of view of sustainable development - not only from an environmental point of view, but also from a social and economic point of view.

The Adaptation Journey

The positive impact
Water management

The aim of the measures used in Botanica K apartment building is to save as much drinking water as possible. This is achieved mainly thanks to the use of gray water - the water from showers, baths and washbasins in bathrooms .

The project is the first residential project in the Czech Republic to use this technology. Experience from the designing, construction and use of the building will now be used to make it possible to add the requirements of the new technology to legal standards and hygiene and building regulations.

Other measures - green roofs or solar panels

The Botanica project is not just about water management. In addition to recycling gray water, Skanska also implemented green roofs to capture and subsequently evaporate rainwater and thus cool the microclimate of the surroundings. Green roofs are built on garages and houses in a total area of 350 square meters.

At the same time, Skanska also worked on energy efficiency. Thanks to this, the apartment building has reached a low-energy standard. The project is 28% more economical than required by law. Specifically, Skanska thoroughly insulated the building, installed quality windows or equipped the common areas of the house with energy-saving LED lighting and energy-saving elevators. In addition, the building uses solar energy to heat water. Solar thermal collectors are located on the roof. A heating strategy to create optimal thermal comfort has also developed.
How does it work?
In the Botanica K apartment buildings which cover an area of 3,000 square meters, 64 apartments have a water recycling system. Thanks to this measure, more than 10,000 liters of quality drinking water can be saved every day.

The water from bathrooms is usually not very polluted. For further use, only basic cleaning processes, such as filtration, degreasing, sedimentation and disinfection, are sufficient. It is then possible to reuse such water for flushing. Even though there is enough gray water, the system is still backed up by rainwater collected in an outdoor underground tank.

This is the reason why two sets of piping were installed in the apartment building. One for drinking water and the other for domestic water. The domestic water is gray water which is, after treatment, pumped from the system in the technical room of the house into the tanks for flushing individual toilets.

Another measure for lowering water consumption in the apartment building is the installation of special fittings, thanks to which the amount of drinking water taken has decreased by approximately 14 %.
Original state
Where the Botanica residential district is now located, there used to be a field. For a period of time during the previous stage of the construction of the residential area, the place was also used as facilities for the building site.
Operation and maintenance
In the Botanica K project, 26 % of the total drinking water consumption was reused in 2018. In concrete numbersthis means that out of the total inflow of drinking water into the house of 4,834 cubic meters, 1,241,000 liters was recycled for flushing toilets. Such a volume of water would be consumed if you filled a bathtub of a standard size of 150 liters every day for 22 and a half years. The saved drinking water equals to 75 full tanks, each with a volume of 16 cubic meters.
Obstacles and challenges
It turns out that standards and regulations do not yet take into account the use of gray water. Skanska is therefore ready to share its experience from this project in the professional community, so that the requirements of new technology can be added to the legal standards and hygiene and building regulations.
How much did it cost?
The total costs of the described measures reached CZK 1,800,000 (EUR 66,000). No grants were used, the entire amount was provided by Skanska.

The return on this investment is expected to be 10-15 years, the operating life of the technology is expected to be 20-30 years.

Savings can already be quantified for the first year of operation of the Botanica K apartment building. Households together saved more than CZK 130,000 (EUR 4800).

Family and apartment houses Water purification and recycling Use of rainwater 

Prague, Czech Republic
2016 – 2018
Skanska a.s.
Skanska a.s.
Skanska Reality a.s.
Gabriela Hlaváčková
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