Sustainable Tip 5 – Is it financially worthwhile to go sustainable for water?


Got to love our oceans

Do you say to yourself something like this: “I can get mains water and sewer and pay about a thousand dollars a year for it.  Why would I spend ten or fifteen thousand dollars, perhaps more, to put in a rain tank or sewage system?”

Here’s the answer I gave myself; maybe it works for you, too?

What are the costs and savings?

My 10,000 litre cement, buried tank and rainwater system cost $11,000.  The recycled sewage system cost $11,000.  I pay no water or sewer bills and no fixed charges. It costs about $100 a year to run the systems.

In 17 years the system has saved me over $17,000 dollars in water bills.


There’s one pump and pipe taking the rainwater to the solar hot water heater, kitchen and bathroom taps and dish washing machine.  There’s another pump and pipe taking recycled, treated water to the clothes washing machine, toilet and garden.  Drawings, data on quality and quantity and equipment are in my book, Sustainable House.


The two systems add value to each other because:

  • By reusing wasted water to flush the toilet and wash clothes and garden with the capacity of the 10,000 litre tank is effectively doubled to a 20,000 litre tank – I’m only using rainwater for drinking and other low water using functions;
  • Daily water use per person is 57 litres, not the Sydney mains water average of 274 litres a person – toilets, clothes washing can take up to half the daily water needs of a person;
  • The amount of water for the waste water system to treat is halved;
  • Fortnightly testing for 18 months shows my water is cleaner than mains water;
  • You love back Earth which gives you free air, almost free water and offers her oceans to absorb your sewage – even offers fish for you to eat there who swim in human waste they can’t avoid – that generosity’s a good thing for me to highly value.  When I go swimming and encounter pollution from others who swim in their own waste I have to admit I don’t thank you.

A sustainable house does so much more than use water efficiently. It nourishes me.  When it rains I feel sweet inside, the sound of the water on the roof reminding me that my house respects that water, is harvesting and using it well.

Even a new house built according to the strictest BASIX requirements would consume an average 156 Litres of mains water per day. Each sustainable house saves two and a half times the mains water of such a BASIX house, with even greater savings compared to new houses in other states. The impacts this has on total mains water consumption:

  • Every 1,000 sustainable houses save as much water as 2,500 BASIX houses; and
  • One sustainable house saves 250,000 litres of mains water per annum, where a BASIX house only saves 100,000 litres per annum.


May the rain drops be with you,



2 Responses to “Sustainable Tip 5 – Is it financially worthwhile to go sustainable for water?”
  1. Michael says:


    Great to hear from you.

    I’m going to add water next week from a tanker unless it rains which seems unlikely.

    By using my treated sewage to flush the toilet, wash clothes and irrigate the garden the 10,000 litre tank here is effectively doubled in size to a 20,000 litre tank.

    But, yes, it’s very dry.

    I pay no fixed charges for water or sewer so pay no water bills. There’s a cost benefit calculator on my site where the payback can be calculated, here:

    Do stay in touch. Oh, I’d love your feedback on the honey harvest video if you have a moment?


  2. Hi Michael,

    How have you gone recently with rainwater? My tanks (10,000L in total) have been pretty much turned off for the last six months. With only 1 day of solid rain, the (efficient) watering of the garden quickly consumed my capacity.

    Do you have a fallback when the water tanks run out?

    Also, am I right in thinking that the biggest cost saving is the fee for connecting to the sewerage system?

    So if people only install the water tanks, the cost equation would look very different?

    Cheers, James

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  • Michael Mobbs

    Michael is a former Environmental Lawyer who is uniquely placed to consult in four main areas:

    • Sustainability Coach and Speaker,
    • Sustainable Urban Farm Design greening, watering and cooling the cityscape, roads, parks, suburbs,
    • Major Projects Consultant Commercial and Industrial,
    • Residential Sustainability Consultant.
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