Greywater facts and figures
• The average person produces around 100 litres of greywater per day1. This amounts to 146,000 litres per year for a family of four.
• 42% of Perth’s mains water supply is used on residential lawns and gardens. This amounts to around 116,000 litres per year for the average Perth household2.
• Savings of 30% on annual household mains water consumption in Perth are achievable with a properly installed greywater reuse unit3,4. In conjunction with plumbed rainwater this can be greater than 50%3.
• The reuse of greywater is approved by the WA Department of Health and can either be by bucketing, direct diversion or treatment1.
• Greywater for irrigation is not subject to watering restrictions.
• Greywater is well suited to provide an alternative and sustainable source of water
for gardens and lawns in Perth5.
• Greywater (and wastewater) reuse support WA State Planning Policies6 as they “Incorporate the re-use and recycling of water, particularly stormwater and grey water, consistent with state water strategy recycling objectives” and Liveable Neighbourhoods7 by “promoting the re-use and recycling of wastewater”.
• In 493 published academic articles on greywater between 1977 and 2012 no negative epidemiological sanitary effects of greywater reuse have been reported8.
• Perth has the second highest per capita water consumption of any Australian capital city9.
• Perth has the second highest typical residential water and sewerage bill of any Australian capital city9.
• Perth has the most energy intensive water supply in Australia, nearly 2.5 times the next highest9.
• Perth has the second lowest amount of water recycling of any major urban centre in mainland Australia9.
Mains water saving scenarios
Assumptions:
Future growth: Average per person water consumption = 79.5kLpa based on 25% reduction on 106kl/p/yr2. Average occupancy = 3. Perth population growth based on 3.5m by 2050.
Existing housing stock: Average per household water consumption = 277kLpa2
Mains water savings for ‘greywater only’ of 25%3,4 and ‘greywater + rainwater’ (plumbed) of 50%2
References:
1. Code of Practice for the Reuse of Greywater in Western Australia 2010. WA Department of Health.
2. Perth Residential Water Use Study 2008/09. Water Corporation.
3. Joshs House Project, real time performance. https://joshshouse.com.au/about-the-
project/real-time-performance/
4. Quantifying the benefits of residential greywater reuse – three case studies from
Perth, Western Australia. J Byrne, S Dallas, A Nayak, M Anda. International
Conference on Sustainable Water Management 2015, Murdoch University, Perth.
5. Small Space Organics, J Byrne. 2012. Hardie Grant Books.
6. State Planning Policy SPP Water Resources 2.9 5.4 (vi). 2006. Government of
Western Australia.
7. Liveable Neighbourhoods. Element 1, Objective 6. Draft 2015. Department of
Planning, WAPC. Government of Western Australia.
8. Greywater Reuse. A Gross, A Maimon, Y Alfiya, E Friedler. 2015. CRC Press, New York.
9. National Performance Report 2017-18. Urban Water Utilities. W12 and W26.
Australian Government Bureau of Meteorology.
