on Wed 25 of Feb., 2009 04:43 EST, by troppo19
posts: 3
I noticed this as an entry, but can't find an associated article ?
Yes, I have thought about this subject - and have also carried out some detailed modelling and analysis. and my conclusion is - rainwater tanks are not cost-effective in North Queensland (and perhaps not cost-effective in many other places either).
The question in Queensland is not so much concerned with whether a rainwater tank is a "good" idea or even a "feel-good" idea. The question is -
is it appropriate to mandate the installation of rainwater tanks for new private dwellings in this region, as required by Part MP (Mandatory Part) 4.2 of the Queensland Development Code?
The modelling referred to is a spreadsheet which includes:
- records all daily rainfall recorded at Townsville airport from August 2004
- a usage calculator for a typical installation complying with MP 4.2 installation and usage specifications
- calculation of of 'tank dry' days and days of tank over-topping under the usage regime.
Summary results as at 9 March 2007.
(This was the last time the model was run, but subsequent runs to the present can be undertaken)
Days elapsed 938
Years 2.6
Annual saving kL 34.5
Annual saving @ $1.55/kL $53.43
Capital cost (2007) $5000
(power and maintenance p.a. not calculated)
Recovery period 93 years
(note: $1.55 is the 'penalty' rate for a kilolitre of water, 2007)
The answer is a resounding NO.
It should be noted that up until recently, the Townsville region has been producing around 2000 detached dwellings per annum. So, if tank installations were mandatory, the additional annual cost of constructing new houses (at 2007 prices) would be $10,000,000, and the annual value of water saved a mere $106,860.
It is as well that the above has assisted in ensuring that a 3 year exemption (to 2010) has been granted for MP 4.2 in this region. There may perhaps be reasons for increasing the large-scale storage of rainwater for future security, replenishment of aquifers etc, but rainwater tanks aren't the answer.
Rainwater tanks and houses
Yes, I have thought about this subject - and have also carried out some detailed modelling and analysis. and my conclusion is - rainwater tanks are not cost-effective in North Queensland (and perhaps not cost-effective in many other places either).
The question in Queensland is not so much concerned with whether a rainwater tank is a "good" idea or even a "feel-good" idea. The question is -
is it appropriate to mandate the installation of rainwater tanks for new private dwellings in this region, as required by Part MP (Mandatory Part) 4.2 of the Queensland Development Code?
The modelling referred to is a spreadsheet which includes:
- records all daily rainfall recorded at Townsville airport from August 2004
- a usage calculator for a typical installation complying with MP 4.2 installation and usage specifications
- calculation of of 'tank dry' days and days of tank over-topping under the usage regime.
Summary results as at 9 March 2007.
(This was the last time the model was run, but subsequent runs to the present can be undertaken)
Days elapsed 938
Years 2.6
Annual saving kL 34.5
Annual saving @ $1.55/kL $53.43
Capital cost (2007) $5000
(power and maintenance p.a. not calculated)
Recovery period 93 years
(note: $1.55 is the 'penalty' rate for a kilolitre of water, 2007)
The answer is a resounding NO.
It should be noted that up until recently, the Townsville region has been producing around 2000 detached dwellings per annum. So, if tank installations were mandatory, the additional annual cost of constructing new houses (at 2007 prices) would be $10,000,000, and the annual value of water saved a mere $106,860.
It is as well that the above has assisted in ensuring that a 3 year exemption (to 2010) has been granted for MP 4.2 in this region. There may perhaps be reasons for increasing the large-scale storage of rainwater for future security, replenishment of aquifers etc, but rainwater tanks aren't the answer.
Regards
Martin Clark