Rainwater Tanks (costing)

The process for undertaking a life cycle costing analysis using MUSIC for rainwater tanks is the same as described in Life-Cycle Costing - Constructed Wetlands.

The origin of all of the ‘expected’ values and algorithms in MUSIC’s costing module, as well as the statistical operations used to generate ‘upper’ and ‘lower’ estimates for rainwater tanks are explained in Table 1.

Note that the CRC for Catchment Hydrology’s survey used to gather real costing information for rainwater tanks from around Australia and to develop the ‘size / cost’ relationships in Table 1 only involved data from small to medium sized galvanized, colorbond, zincalume and aquaplate above ground tanks of various shapes. Costing information for polyethylene (plastic) tanks is provided in Taylor (2005b), Appendix H: Costing information and from several Australian rainwater tank suppliers’ web sites.

Table 1. Summary of cost-related relationships for rainwater tanks.

Element of Life Cycle Costing Model	Default Option for Estimation in MUSIC	Alternative(s)	Notes
Life cycle	25 years.	No alternative in MUSIC.	Default value from Melbourne Water (2003) and relevant to metal, aboveground tanks. Estimates vary from 10 to 100 years depending on tank materials. It is recommended that users contact their tank suppliers to estimate the life cycle if they have a specific type of tank in mind. Upper and lower estimates have not been provided in MUSIC.
Total acquisition cost (TAC)	TAC/kL ($2004/kL) = 1,354 x e[(-0.1589) • (Vol)] R2 = 0.63; p = < 0.01; n = 35. Where: Vol = volume of tank (kL or m3); and e = 2.718.	No alternative size / cost relationships in MUSIC. For literature values, see Taylor (2005b) - Included in Appendix H or contact tank suppliers.* NB: Appendix H includes some approximate acquisition costs for plastic tanks (i.e. 0.5 to 48 kL in size)	Warning: The default relationship should only be applied to galvanized, colorbond, zincalume and aquaplate aboveground tanks, 1 to 10 kL in size. (NB: Underground tanks are generally more expensive to purchase and have longer life cycles.). TAC includes plumbing and installation costs (i.e. to connect tanks to toilets or hot water systems) but not GST. Note that an unexpected finding from the CRCCH dataset is that the predicted TAC costs rise as the tank size moves from 1 to 6 kL in size (as expected), but then slightly falls from 6 to 10 kL (unexpected). Upper and lower estimates derived using a 68% (or 1 standard deviation) prediction interval for the regression.
Typical annual maintenance (TAM) cost	TAM ($2004) = 90.	No alternative size / cost relationships in MUSIC. For literature values, see Taylor (2005b).*	Upper and lower estimates have not been provided in MUSIC due to limited data. This TAM estimate is based on: $75 for annual maintenance (from Kuczera and Coombes, 2001), scaled to $2004 using an annual inflation rate of 2%, plus $10 per year for operation and maintenance cost associated with pumps. Estimated using information from: Gardner (2004) and Grant and Hallmann (2003) on electricity use and cost that when combined, indicate pump running costs are typically $0.41 per kL; and Duncan (2004) who suggested a typical residential water usage rate for rainwater tanks would be approximately 20 kL per year. This TAM estimate assumes the tank is plumbed into a house (e.g. for toilet flushing) or the garden and includes a pump.
Annualised renewal / adaptation cost (RC)	RC ($2004) = $0	No alternative size / cost relationships in MUSIC.	Assumed to be minor and included in TAM.
Renewal period	N/A (as RC = $0)
Decommissioning cost (DC)	DC ($2004) = $200	No alternative size / cost relationships in MUSIC.	Estimate obtained from a NSW plumber as no data was found in the literature. Given the low cost and effect of discounting in the life cycle analysis, the influence of any error associated with this estimate will be negligible.
General caveats / notes for this type of device	* Up to date acquisition cost estimates for rainwater tanks are easily obtained from the internet or directly from tank suppliers (for a list of suppliers see www.wsud.org/wsud.htm). This industry is rapidly evolving in Australia, so obtaining current estimates is recommended.