Case study: Clay Farm water reuse scheme
The Clay Farm development in Cambridge
Cambridge City Council’s ‘Clay Farm’ site is an example of an innovative approach to onsite water reuse, one of the case studies being explored by the Enabling Water Smart Communities (EWSC) project, supporting the project’s ‘enabling action’ around onsite water reuse
The Clay Farm project is a development in Cambridge with 208 homes and commercial accommodation. The residential accommodation is arranged in a grid of quads surrounding a park at the heart of the site. Each quad consists of 23 homes ranging from one to three-bedroom apartments and family houses. Each home has a private patio garden. In the heart of each quad is a moat that can store and attenuate rainwater.
Onsite Water Reuse
At Clay Farm, the rainwater is fed through a reed bed where natural processes remove pollutants before entering a 240m³ concrete tank. From there, the water is pumped into a small holding tank installed in a central plant room.
The water then undergoes further treatment, including the use of ozone to remove bacteria and viruses. It's then transferred into a break tank, which includes an emergency mains water top-up for periods of low rainfall. A triple booster pump set then pumps the water to all WCs in the development through a dedicated non-potable water pipe network.
The rainwater harvesting is fully remote-controlled including pressure measurements, water quality monitoring and fault reporting allowing remote diagnostics and maintenance on demand.
Clay Farms: A closer look
One of the key organisations behind developing this site was Aquality, specialists in supplying and installing water reuse solutions, and very supportive of an integrated water management approach. We spoke to Lutz Johnen, Managing Director, for his insights on the Clay Farm development, and what lessons we can learn from this case study.
Why is the Clay Farm development unique from a water perspective?
Cambridge Council have been pushing for local schemes to achieve the highest Code for Sustainable Homes (CfsH) level (level 5), something which we are very happy to support. Level 5 aims to achieve a water usage in the development of around 80 litres per person per day (l/p/d).
Clay Farm represents a unique approach to rainwater harvesting as water is also harvested from hardstanding as well as roofs - hence why we call it a ‘stormwater’ harvesting system. This stormwater from roads and walkways requires further treatment, which was incorporated at Clay Fram via a reed-bed – something which could be considered a Sustainable Drainage System (SuDS) feature.
Who else was involved in the project?
Planning and design for the site was carried out by Pollard Thomas Edwards. Construction was via Hill Construction for Countryside Properties.
Hill Construction then employed Aquality for the water reuse design, and the M&E contractor TClarke commissioned Aquality to provide and install the rainwater systems for the total project. Aquality worked closely with AECOM to design and install this rainwater system.
The EWSC project team joined others on a recent site visit to the Clay Farm site
What have been some of the challenges and how have these been overcome?
It was certainly a challenge to collect sufficient non-potable water to be able to achieve CfsH Level 5. We overcame this by collecting water over a greater area. This then turned the challenge into one of water quality, due to collecting rainwater runoff from different surfaces. We tackled this challenge by installing an additional treatment reed-bed and carrying out water ‘polishing’ (further treatment) in the on-site plant room.
What lessons can we take forwards to similar schemes?
Incorporating drainage and flood management into the design is key. As the rainwater collection forms part of the system efficiency, this should be given more thought in the planning process.
Additionally, part of the drainage and collection system at Clay Farm is leaking. Reducing performance (estimated at 40%), as not all water reaches the collection tanks. We’re looking to improve the collection system design in in future developments.
Any other thoughts you'd like to share about this case study?
Despite the leaks I mentioned, the Clay Farm development is a simple system with good efficiency. Maintenance requirements are low, meaning that it’s a very cost-effective system once installed. Overall, this system has an estimated water saving of 20-25l/p/d.
Residents are aware of the system and have not complained since in use – I take this as a positive sign!
EWSC and Onsite Water Reuse
Onsite Water Reuse is one of the key workstreams that form the EWSC project. This workstream is focused on supporting water companies and government in their quest to deliver water reuse within residential developments through three components:
Regulations for water reuse
A Roadmap for water reuse
A Business case for water reuse.