After a citizen participation process, a combination of a chlorine pool and a natural swimming pool was created in the Stadionbad Bremen in the year 2006. In the swimmers’ and diving pools, water purification is conventional, whereas in the non-swimmers’ pool and in the children’s area, biological water treatment is integrated using several Neptune filters. The splash pads are also provided with water from biological water treatment. The total usable water surface of the natural pool area is 2,560 m². These pool areas can be fed with a maximum of approximately 820 m³/h of treated water from the Neptune filter. With a total volume of about 2,600 m³, the pool water can be circulated approximately every three hours at maximum output.