Earthship Te Timatanga (greywater)

Name of case study

Earthship Te Timatanga (greywater)

Location

  • Hikuai
  • Coromandel Peninsula
  • New Zealand

Location

2015

Scale

Building / single site

Area / size

240m2 building on 1 hectare

NbS employed

Bioremediation / phytoremediation of water

Type of NbS

Hybrid living/engineered interventions

Initiator

Sarah Rowe and Gus Anning

Funder

Sarah Rowe and Gus Anning

Budget

NZ$1,200-$1,400 per m2

Design group

Building Designer: Harriet Pilkington, Young and Richards. Consulting architect: Graeme North, Graeme North Architects. Earthship building consultants: Ben Garratt, Rosa Henderson, Sculpted Earth.

The greenhouse in Te Timatanga. Photo from Facebook “Earthship Te Timatanga”
The greenhouse in Te Timatanga. Photo from Facebook “Earthship Te Timatanga”
Climate change benefits
  • Water availability
  • Reduced air quality
Societal / socio-cultural benefits
  •  Pressures of urbanisation
  • Water security and quality
  • Food security and quality
Ecological benefits
  • Aesthetic value
  • Decomposition
  • Food production (for humans)
  • Fresh water
  • Habitat provision
  • Nutrient cycling
  • Purification (of water, soil, air)
  • Relaxation and psychological well-being

Summary of case study

This nature-based solution is part of the north-facing atrium of an earthship. Earthships are houses made of natural and recycled materials with a specific building design to enable off-the-grid living. The design includes a greenhouse for temperature regulation, food production and water treatment. It is constructed by using double-glazed glass with a specific angle and orientation towards the sun depending on the local climatic conditions (Freney, 2013).

Rainwater is collected in cisterns and used as the water supply for the house. The atrium/greenhouse is used to treat greywater. It is built on an angle so that the water is pulled down through the garden by gravity. On the high side, the water passes through a coconut filter before entering the garden. The filtered water is then collected and redirected for secondary purposes, either flushing the toilet or watering crops. A 12V bilge pump has been installed to control the water flow, but according to the owners it is rarely necessary to use it because the water flows through the system naturally. The blackwater is treated using a NaturalFlow WORMORATOR® and is then used to irrigate crops. 

Potable water is an increasingly scarce resource. Currently, potable water is not only used for drinking but also often used for purposes which do not require such clean water. The natural filtration system ensures the local and efficient use and recycling of water and nutrients. This reduces the pressure on potable water resources, which in turn facilitates adaptation to climate change (Castellar et al., 2022). In dense urban areas grey water reuse could lead to a 30% reduction in water consumption (Boano et al., 2020).

Decentralised water reuse as opposed to a centralised sewage system generally requires less energy and has less structural costs (Castellar et al., 2022). As this system largely depends on forces of gravity and has little piping, it indeed uses less energy and materials. Additionally, the planter provides carbon sequestration and local nutrient cycling through the growing plants. The way the greenhouse is built, it provides passive heating and temperature regulation of the house. This further decreases the energy needs of the house and thus decreases GHG emissions.

For the inhabitants, the planter enables local water sourcing and cycling. The planter is also used to grow food. Both of these support the preferred off-the-grid and sustainable lifestyle of the owners. On a bigger scale, the decentralised water treatment prevents sewage pollution into the local environment. It also reduces the costs associated with centralised water treatment and reduces the pressure on local potable water sources (Castellar et al., 2022). 

Māori have always employed extensive waste management systems (Pauling & Ataria, 2010). Human waste is considered tapu (forbidden, spiritually unsafe) and discharge of human waste directly into freshwater sources harms its mauri (life force). Water can only become noa (unrestricted, safe, good) through contact with Papatūānuku, The Earth Mother (Simmonds et al., 2019). Here the water quality is restored by contact with earth.

The greenhouse garden creates habitat for small local animals such as spiders and skinks. The surplus of treated water is used to water plants, so the freshwater influx in the area is increased without ‘wasting’ potable water. Both of these decrease some of the pressure of climate change on the local ecosystem.

Horizontal flow wetlands like these require 3-10 m3 space per person and the inlet filter needs to be replaced at least every 10 years (Cross et al., 2021). After an initial investment, this house has minimal monthly costs due to its self-sustaining water and energy usage. The water costs in the Coromandel are $1.37 per m3 of water with an extra fixed rate of $NZ667 – $1100 per year (Thames-Coromandel District Council, 2023).  In Aotearoa New Zealand, each person uses about 159L of water in winter and 231L in summer per day. About 15-20% of this water is used for flushing toilets (Pollard, 2022). On top of the fixed rate, the water costs would be about $400 each year. Te Timatanga is completely self-sustaining in terms of water, thus saving hundreds of dollars per year. The house has a similar price per m2 as water costs would be per year. The prices for water are only expected to increase further, so this is a good long term investment.
The planter also provides various other benefits, such as cleaner air, a pleasant interior environment and food provision. Cross et al. (2021) have shown the value cases of many other nature-based solutions for waste water treatment.

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References
  • Boano F., Caruso A., Costamagna E., Ridolfi L., Fiore S., Demichelis F., Galvão A., Pisoeiro J., Rizzo A., Masi F. (2020). A review of nature-based solutions for greywater treatment: Applications, hydraulic design, and environmental benefits. Sci Total Environ. 711:134731. doi:10.1016/J.SCITOTENV.2019.134731.
  • Castellar J.A.C., Torrens A., Buttiglieri G., Monclús H., Arias C.A., Carvalho P.N., Galvao A., Comas J. (2022). Nature-based solutions coupled with advanced technologies: An opportunity for decentralized water reuse in cities. J Clean Prod. 340:130660. doi:10.1016/J.JCLEPRO.2022.130660.
  • Cross K., Tondera K., Rizzo A., Andrews L., Pucher B., Istenic D., Karres N., McDonald R. (2021). Nature-Based Solutions for Wastewater Treatment. A series of factsheets and case studies. London: IWA Publishing. https://issuu.com/viviboe/docs/00_natusan_publication_final.
  • Freney, M., Soebarto, V., & Williamson, T. (2013). Earthship monitoring and thermal simulation. Architectural Science Review, 56(3), 208-219. 
  • Pollard, A. (2022). BRANZ Study Report SR469 Residential water use in New Zealand.
  • Smith, C. (2017). Houzz Tour: Earthship Te Timatanga. Houzz NZ. Available online: https://www.houzz.co.nz/magazine/houzz-tour-earthship-te-timatanga-stsetivw-vs~83031011. Date accessed 10 May, 2024.
  • Pictures from  “Earthship Te Timatanga” facebook, with permission
  • https://www.facebook.com/Granddesignsearthshiptetimatanga

Further resources:

Earthship Te Timatanga (atrium)

<< Bioremediation / phytoremediation of water