From the roof on the green block (Block B) the rainwater is led down into 2 tanks under the ground. These tanks contain a total of 11 m³. Hereafter the rainwater from the tanks is used for toilet flush. When there is a lack of rainwater in the tanks, the water will be thinned-down by the ordinary water supply.

3 floaters connected to the buildings CTS-system are mounted in the tanks. The first floater signals when there is only 1 m³ water left in the tank. The second floater reacts when there is only 1,5 m³ water left in the tank and water will be thinned down. The third floater stops the water supply when there is 2 m³ water left in the tank.

It is very important that the water is stored under the ground where it is dark and the temperature constantly 8^o C. If the water is stored in a light and warm environment it will rot and cannot be used by the residents.

Measurements show that the flats in the Block B use almost as much hot water as the flats in Block A (the conventional block). However, the consumption of cold water is 50% less in the Block B compared to Block A. According to the measurements half of the consumption of cold water in the environmentally friendly block is covered by rainwater.

The amount of rainwater only covers approx. 25% of the total water consumption in Block B and does not live up to the expectations which was estimated to 67% of the consumption. Still the report from the University College of Aarhus concludes that the plant is running satisfactory and that the total economy of the plant is very positive if measured over a period of 20 years.