**4. Conclusion**

This chapter presents a computing tool that can be used to examine the water savings potential and financial viability of a rain water harvesting system in a multi-storey building. A case study is presented for a 75kL rainwater tank, located in Sydney, Australia. It is found that the performance of a rain water harvesting system in terms of water savings improves significantly with the increasing roof size and water demand. It is also found that for most of the typical scenarios the rain water harvesting system is not financially viable at the current water prices in Australia, which is highly subsidized and in the current high interest regime (greater than 7%). In a few cases however, the rain water harvesting system is likely to be financially viable, in particular at smaller interest rates and higher water prices. It is also found that the capital cost represents the highest component in the whole life cycle cost of a rain water harvesting system followed by the maintenance cost. The outcomes of this study suggests that government authorities should consider increasing the subsidy for a rain water harvesting system to offset the financial burden of the home owners to encourage the installation of rain water harvesting systems. It should be noted that there are significant environmental benefits of a rain water harvesting system such as water conservation and on-site retention of pollutants. Rainwater harvesting system also increases the resilience of the urban water supply system, which is important during drought years, which is common in Australia. Rainwater harvesting system is also likely to defer construction of major water supply dam and desalination plant.

### **5. References**

176 Urban Development

Fig. 22. Annual benefits and costs of the best possible scenario for the rainwater harvesting

A breakdown of the different cost components of the whole life cycle cost is presented in Table 2. It can be seen that the capital cost comprises the highest component (66%) whereas the maintenance cost is the second highest contributing 18%. The pump operating cost only contributes 6% of the total cost although when added to the pump capital, replacement and maintenance costs the total expenditure of the pump jumps to \$9,872 or 19% of the total life cycle cost. This is quite significant and whether or not a rooftop rainwater tank is justified may be a subject to further research as with a rooftop tank there would be no pump cost. Although, the weight of a 75kL rainwater tank is likely to add significant structural cost to

Cost item Life cycle cost (Aus\$) % of whole life cycle

Capital \$34,575 66 Replacement \$4,151 8 Maintenance \$9,375 18 Pump operating cost \$2,847 6

> GST \$1,222 2 Total \$52,173 100

Table 2. Breakdown of whole life cycle cost for the best possible scenario of the rainwater

This chapter presents a computing tool that can be used to examine the water savings potential and financial viability of a rain water harvesting system in a multi-storey building.

cost

the building which may not justify a rooftop rainwater tank.

system

harvesting system

**4. Conclusion** 


**Part 3** 

**Cultural Heritage and Urban Development** 

Tam, V.W.Y.; Tam, L. & Zeng, S.X. (2009). Cost effectiveness and trade off on the use of rainwater tank: An empirical study in Australian residential decision-making. *Resources, Conservation and Recycling*, Vol. 54, pp. 178-186.
