Harvest Festival at Roof Water Farm


We got to know the Roof Water Farm in 2014 when the two founders Grit Bürgow and Anja Steglich gave a presentation about urban water management at our temporary garden Little Wood. It was a memorable afternoon because of its beauty and now, three years later, I was invited for the harvest festival at Roof Water Farm. I was as curious as much as I was excited and I finally took my time to visit the farm. When I arrived at block 6 on Bernburger Str. 22 in Kreuzberg I was surprised because of several reasons. The first thing I noticed was that the farm was not on the roof. And also, the harvest was not quite what I expected:  instead of salads, herbs or berries, we had smoked fish and gherkins. I loved it! But more of that later.

The Roof Water Farm at its current state is a pilot of a greenhouse that is applicable on residential, office, school or hotel buildings. It uses the recycled wastewater of buildings as a resource for producing food with an aquaponic and hydroponic growing system. But it is also much more. It is a research and education project that aims to change the awareness and the management of water usage in cities.


When it comes to water in our cities we mostly think of clear and dirty water. But we tend to forget all the tones of grey water in between that are very precious. If we gave up our black and white thinking patterns we could have a much more natural, fluid, fruitful and effective water management. At the Roof Water Farm I got to know a specific organic water cleaning method. But what is maybe even more important is what happens before and after the cleaning.

Let me explain a little about the background to all this. What happens in our normal wastewater plants is unfortunately an enormous waste of energy and resources. All water, be it from hospitals or regular households, from the toilet or the shower and even rainwater goes to the same canalization and from there to the plant. This is a pity because most of the water actually gets more dirty in the canalization. The expenditure of energy (and money) could be much lower if we separated the water (just as we already do with our trash) before it gets treated. Currently, the processing of wastewater in Berlin consumes as much energy as a whole city with 280.000 residents. Now, after the water is treated in the conventional wastewater plants the dirt mud that comes out of the water gets burned. This again is a loss of highly useful nutrients that are contained in wastewater and that could be used as fertilizer for agriculture. And then the next question comes up: do we really need water with drinking water quality to flush down our shit in the toilets? Maybe it would be useful to treat the water in different ways and keep it separated after the treatment for specific usage.


The project that is now summed up under the name Roof Water Farm challenges those issues in a productive way. The pilot plant test side started in 1987 long before it got its current name. In the frame of the International Building Exhibition a wastewater system was developed in a building complex in Kreuzberg (block 6) that separated the blackwater (from the toilets) and the greywater (from the sinks and showers) of the 250 residents. The blackwater went to the canalization. The greywater went to a reed bed in the backyard where the water was naturally cleaned and vaporized by reeds. Reed beds are nowadays still used for rainwater collection and evaporation to improve the microclimate. In 2006 the system got reworked. On top of the former polishing pond a water processing house was built and the greywater was treated there mechanical-biologically to the quality of  bathing water and got reused to flush the toilets of the residents. In 2013 the actual Roof Water Farm was born. It is one answer to the question of how to make use of the precious resource water in times when resources get scarcer.

So, let’s start again. The Roof Water Farm includes a water processing house and a greenhouse where food is grown with the recycled wastewater of the residents. In the greenhouse are two different systems to grow the plants: aquaponics and hydroponics. Both systems are water based that have no need for soil. The aquaponic system uses service water produced out of grey water and a fish tank. The fish fertilize the water with their excretions, which is afterwards run through the growing tubes and goes back to the fish tank. A circle. The hydroponic system is run with goldwater. Goldwater is made from the blackwater (toilet water) from the residents. This is a new innovation by the Roof Water Farm project and was introduced on site in 2014. Therefore the blackwater is treated and reduced but still contains all the npk nutrients (nitrogen, phosphorus, potassium), which is highly potent and needed to feed the plants. Goldwater has a golden color but could also be just as valuable as gold when it comes to agriculture.


Of course, the hygiene standards are extremely high when working with waste water. Roof Water Farm produces safe service water and fertilizer products out of wastewater in the first step before it is entering the food production systems. The water is monitored constantly and the plants and fish are sent to the laboratory regularly to prove the absence of pollutants. The results so far meet the official standards. You can find more information about that topic on the website of the Roof Water Farm.

Combining wastewater separation, mechanical-biological water treatment and urban farming could help to solve some of the big issues with which we are confronted more and more. It could help reducing the waste of water, resources and energy. Further it offers solutions for urban farming for an ever growing demand of food. Producing the food this locally again helps to save energy. First calculations show that the potential of Roof Water Farm greenhouses if run commercially or intensivly managed can cover 86% of the need of vegetables and fish of the urban residents.

Until the Roof Water Farms will be on the rooftops of Berlin (and other cities) we have to remain patient. There are still some steps to go in order to change the perception of the authorities and of the people. This is why the Roof Water Farm is also an education project as well as everything else. In my case it worked.


Back to the harvest festival from last week. Visitors got tours through the water processing house and the greenhouse. But moreover we could taste the harvest: smoked fish and gherkins. The cucumbers were grown in the greenhouse obviously. So was the fish, the actual harvest of the festival. Since the greenhouse has no heating system yet, the fish had to be eaten before the water in the tanks would freeze. However, it was delicious.


Leave a Comment

You must be logged in to post a comment.