„Hamburg Water Cycle“: A sustainable solution for water management
The continuous movement of water through its various phases and states, which we know as the water cycle, is an essential component of our ecosystem. This natural process not only ensures the survival of all life on our planet, but also plays a crucial role in human society, particularly when it comes to water management.
In this blog post, we will take a closer look at the concept of the “Hamburg Water Cycle” using our residential project “Jenfelder Au” as an example – an innovative initiative for sustainable water management in housing developments.
What is the water cycle?
Before we focus on the “Hamburg Water Cycle,” let’s take a quick look at the Earth’s natural water cycle. Water constantly moves between the air, rivers and lakes, soil and rock, and living organisms. This cycle has no fixed timeline and includes processes like evaporation, condensation, precipitation, infiltration, and runoff.
The journey of water
Evaporation
The water cycle begins with the evaporation of water from oceans, lakes, rivers, and other bodies of water, driven by solar energy. As the sun warms the water’s surface, water molecules turn into vapor and rise into the atmosphere.
Condensation
Once in the atmosphere, the water vapor cools and condenses into tiny droplets or ice crystals, forming clouds.
Precipitation
When clouds become saturated, the water falls back to the Earth as rain, snow, hail, or sleet.
Infiltration & Runoff
Much of the precipitation soaks into the ground, where it is filtered through soil layers and stored as groundwater. The rest flows back to the sea via rivers and lakes, completing the natural water cycle.
Why is the water cycle important?
The natural water cycle is vital for the health of our ecosystem. It not only provides water for plants, animals, and humans, but also helps regulate the climate and maintain global water supplies and ecosystem stability.
The total amount of water on Earth remains constant. No new water is created. This makes it essential to manage water resources sustainably to meet the needs of both current and future generations.
The “Hamburg Water Cycle” – reusing water in the residential district
Building on the natural water cycle, HAMBURG WASSER has launched a project to make water management more efficient and sustainable: the "HAMBURG WATER Cycle".
But what does this actually involve?
Supported by funding from the Federal Ministry of Education and Research, the Federal Ministry for Economic Affairs and Energy, and the EU LIFE+ programme, the "HAMBURG WATER Cycle" is an innovative approach to optimizing the water cycle in urban areas.
How the “Hamburg Water Cycle” works: reusing blackwater, greywater, and rainwater
At the heart of the "HAMBURG WATER Cycle" is the recycling and reuse of blackwater, greywater, and rainwater.
Blackwater is wastewater from toilets and kitchens that contains high levels of organic matter. It is heavily contaminated and requires thorough treatment before it can be returned to the water cycle.
Greywater, on the other hand, comes from bathtubs, showers, sinks, and household appliances. It is less polluted than blackwater but still needs treatment before reuse. Greywater can be recycled for toilet flushing, irrigation, or industrial processes.
Rainwater, by contrast, is collected from roofs, streets, and other surfaces and is often discharged unused into the sewer system. In the "HAMBURG WATER Cycle" concept, it is treated as a valuable resource that can be used for irrigation or allowed to infiltrate the ground to replenish groundwater in the natural water cycle.
Best practice: the “Hamburg Water Cycle” in the Jenfelder Au residential project in Hamburg
The effectiveness of the "HAMBURG WATER Cycle" is demonstrated by its implementation in the "Jenfelder Au" neighborhood in Hamburg's Wandsbek district. This innovative residential project is a joint venture between OTTO WULFF and cds Wohnbau, spanning three building plots and approximately 200 apartments.
The central component of the "HAMBURG WATER Cycle" in the "Jenfelder Au" project is the separate treatment of different types of wastewater, also known as partial flow treatment. Rainwater, blackwater, and greywater are collected individually and treated for reuse.
For the blackwater cycle, special vacuum toilets were installed in the apartments at "Jenfelder Au" to concentrate the wastewater. This blackwater is then separated and transported using a vacuum system. At the "Jenfelder Au" treatment facility, the substances in the blackwater are fermented in a biogas plant with a combined heat and power system, generating heat and electricity for the district simultaneously.
This is the first time in Europe that toilet wastewater has been used on-site to generate energy on such a large scale. The remaining residues can be used as fertilizer, closing the district's water, energy, and nutrient cycles. The less polluted greywater is transported via a separate pipe system to the district's treatment facility, where it is cleaned efficiently and either discharged or reused as process water.
Rainwater is managed with specially designed retention basins, where the water is collected and allowed to evaporate. This system helps maintain a pleasant microclimate in the district and creates opportunities to "live by the water".
In conversation with our technical project manager Nicolas:
1. Why was it decided to implement the "HAMBURG WATER Cycle" during the project planning, and what were the ideas behind it?
OTTO WULFF chose to plan several construction sites in the Jenfelder Au together with a long-standing joint venture partner because the Jenfelder Au is one of Hamburg's largest and most exciting redevelopment areas.
In connection with the HAMBURG WATER Cycle, these project developments offered the opportunity to be part of this pioneering initiative and to integrate sustainability into the built environment.
2. What were the main challenges in implementing the "HAMBURG WATER Cycle" in a residential project of this size, and how were they addressed?
The vacuum drainage system reduces the amount of flushing water needed and therefore the dilution of the recyclable materials it contains, making them usable. From a technical perspective, this created specific acoustic challenges that had to be carefully considered during planning. During construction, our on-site colleagues focused on precise execution and avoiding sound bridges.
During planning, we worked closely with an acoustic consultant and paid special attention to verifying all relevant details. On site, the construction management team ensured everyone was aware of the requirements and carefully checked every toilet installation, including the associated pipe routing.
3. How has the "HAMBURG WATER Cycle" concept impacted water usage in Jenfelder Au, and what are the benefits for residents?
The most obvious advantage is reduced water consumption. A conventional toilet uses on average 3 to 6 liters per flush, while a vacuum toilet uses only about 1 liter.
The conscious use of water as a resource was emphasized throughout the project, with rainwater partially routed above ground and incorporated into the design of outdoor spaces. This allows even the youngest residents to experience water first-hand, fostering an appreciation for the resource from an early age.
