Taps and Showers
The Living House has used two 25,000L concrete water tanks (provided by Dart Concrete) to supply all of our potable water needs. This rainwater tanks will collect rainwater from the roof of the main dwelling and store it for future use.
The cost of providing water tanks to fully supply a dwelling's potable water requirements is not insubstantial. However often the capital cost of a technology, such as rainwater tanks, is recouped through the reduced cost of a service over the lifetime of the system, usually called the pay back period.
Unfortunately for us this does not necessarily provide us with any cost savings in terms of our Watercare bills as we have no option of connecting to the Watercare network at this time. However even if we did have the option of connecting to the Watercare system (and thus potentially saving on water bills) we actually believe that we would be financially better off still connecting to this network rather than including rainwater tanks as part of their project, as the payback period for a rainwater system to satisfy the entire water demand for the Living House is quite long.
For example our estimated cost of installing 50,000L of rainwaters for the Living House is as follows:
Heavy duty water tanks (suitable for burying under the driveway) - $12,606
Excavation for water tanks - $5,000
Plumbing of tanks to house for rainwater collection (drainlayer) - $2,000
Plumbing of tanks to house for rainwater use (plumber) - $1,000
Electrical supply for pump - $1,000
Supply and installation of pump - $1,000
Total cost - $22,606
According to BRANZ (1) the average Auckland household uses around 150,000 litres of water a year and typically buys all of that from Watercare at a cost of $2.454 per 1000 litres (or $368 per year for 150,000L).
At the above usage cost of $368 a year the installation of our rainwater system will take 61 years to pay itself off. Not really financially worth it is it. Based on the current cost of water in New Zealand the economics of rainwater tanks does not appear to stack up.