What's unusual in this house is that we drink rainwater in preference to mains water, right in the heart of the city.
I wanted to collect all of the water the family needed from off our roof. We
had never been big water users, despite running the washing machine daily
and doing all the other normal things
a family of four does. Even before renovating we used just 350L of water
a day; about half that of the average Sydney household. But this still adds up to around 100,000L of water annually.
For the 21 years from 1996 to 2018 the average daily water use for 4 people is 57 litres per person, or 84,000 litres a year. The average daily recycled water use was 96 litres when the two children were 6 and 10 in 1996 and the washing machine went every other day, now it's around 50 lites. Because the recycled water is just that - going back into the tank from which it's been pumped when it's used to flush the toilet or wash clothes - the capacity of the holding tank for recycled water is only 200 litres.
My rainwater has been tested regularly, and is safe to drink: in fact, it is actually cleaner than mains water. I've achieved this by using a 'first-flush' device (to divert the first, dirty rush of rainwater from the roof), a sump and self-cleaning gutters.
Every day more than three million Australians, mostly in rural areas, safely drink rainwater. But at the time that I disconnected from Sydney's mains water and relied solely on rainwater, no one knew about the quality of Australia rainwater in cities. As far as I know, my family was the first to be assessed according to scientifically verified and published data.
ENSURING WATER QUALITY
Tests on our drinking water carried out by the University of Technology, Sydney, have demonstrated consistently low turbidity and faecal coliform counts. Of particular importance in an urban setting, lead levels recorded in our tank water have been shown to be below the safety threshold recommended by Australia's National Health and Medical Research Council.
How is it possible to achieve clean water with almost no maintenance when surrounded by busy roads used daily by thousands of trucks and cars and with planes flying overhead to and from Australia's busiest airport? It's really quite simple and my Sustainable House has four clever adaptations to produce fresh and safe water:
- the enclosed gutter on the
roof excludes leaves and bird droppings but lets water in
through special sinks
- the downpipe contains a sloping mesh trap to exclude leaves and debris without blocking water flow
- a simple diversion system in the downpipe directs the first 6-10L
of rainwater (carrying dirt from
the roof) away from the water tank and into the garden, and
- a sump with a fine mesh excludes the last of the heavy sediments before the water enters the tank
The guttering system feeds into a concrete tank that holds about 8500L and is hidden below our home's back deck. When it's full the water overflows into a mini-wetland to reduce stormwater runoff from the block.
MAXIMISING YOUR RAINWATER SYSTEM
The tank system functions extraordinarily well but we have run out of rainwater four times, which has meant popping across to the neighbours to occasionally "borrow" 1500L of water. Installing a bigger tank would have alleviated this problem, but not solved it: there simply isn't enough rainfall coming off our tiny roof to sustain a family of four. It would be enough for two.
This shortcoming aside, the system has served us well and means an extra 100,000L of fresh water remains in Sydney's main dam supply each year.
To get the most value from your
rain-tank investment you need to
use the water efficiently. And the
key, in this driest of countries, is
to re-use as much water as possible.
When it's re-used endlessly for gardening, toilet flushing and
clothes washing (see how in my
chapter on Wastewater), two big
wins come your way.
You don't depend on rain to flush your
toilet (because filtered flush water comes back repeatedly to be used for that purpose), and you don't need as big
a rain tank. This means you use the
best-quality water - rainwater - as efficiently as possible.
When you see clean, precious rainwater stored in rarely filled rain tanks used to flush toilets, you'll appreciate how wasteful it is to use cloud-carted water to flush toilets just once. What an abuse of the rich, intermittent gift bestowed on our roofs!