**1. Introduction**

158 Urban Development

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Al-Bassam (2011): Application of ERT survey for addressing the issues of urban rain storm water logging in the Qassim province of Saudi Arabia. Submitted to the Australia is one of the driest inhabited continents, with highly variable rainfall. A growing urban population and frequent droughts in recent years have made water supply a major issue in Australia. A number of alternative water sources have received attention in Australia including rainwater harvesting, grey water reuse and wastewater recycling. Among these, rainwater harvesting has received the greatest attention as rainwater is fresh in nature and can be easily collected and used for non-potable purposes. However, many Australians still show a reluctance to adopt rainwater harvesting systems. Statistics from the Australian Bureau of Statistics (ABS) show that about 47% of respondents say that the main reason for not installing a rainwater tank is the perceived 'higher cost' (ABS, 2011). Government authorities in Australia provide financial incentives to encourage home owners to install rainwater tanks. For example, Sydney Water Corporation in Australia offers a rainwater tank rebate of up to \$1,500 (here \$ is in Aus\$) depending on the size of the tank installed and the type of water use.

Many home owners do not readily see the benefit of a rainwater harvesting system over the long term, which may be attributed to the limited understanding of the life cycle costs of the system. Domenech and Sauri (2010) investigated the financial viability of rainwater harvesting systems in single and multi-family buildings in the metropolitan area of Barcelona (Spain). In single-family households, an expected payback period was found to be between 33 to 43 years depending on the tank size, while in a multi-family building a payback period was 61 years for a 20 m3 tank. Imteaz et al. (2011) found that for commercial tanks connected to large roofs in Melbourne, total construction costs can be recovered within 15 to 21 years depending on the tank size, climatic conditions and future water price increase rate. Tam et al. (2009) investigated the cost effectiveness of rainwater harvesting systems in residential areas around Australia and found that these systems can offer notable financial benefits for Brisbane, Sydney and the Gold Coast due to the relatively higher rainfall in those cities as compared to Melbourne.

Notable research has been conducted on the relationship between rainwater tank sizing and water savings. Khastagir and Jayasuriya (2009) used water demand and roof area to develop a set of dimensionless number curves to obtain the optimum rainwater tank size for a group

Rainwater Harvesting in Large Residential Buildings in Australia 161

The daily rainfall station's data from the study area is

needed.

Exit the program.

Example in Figure 1.

Example in Figure 2.

Tank sizes covered range from 10 kL to 100 kL. Example in Figure 3.

This helps to interpret the

If the BCR > 1, the rainwater harvesting system presents a

User needs to select a particular tank size.

Example in Figure 4.

Example in Figure 5.

results.

net saving.

Main menu Submenu Function Description

for the study area.

Exit This allows the user to exit the program.

water demand.

LCCA Input This allows the user to enter

installation costs.

Figure 3.

rebates.

Table 1. Main menus and submenus of RWTAM model

each tank size.

This allows the user to select the relevant daily rainfall data file

This allows the user to enter data

(for calculating rainwater savings) such as lot size, roof area, number of occupants and

various input data for cost analysis such as capital cost, government rebates and

This function produces an average annual water savings vs. tank size plot as shown in

This function presents the annual average water savings in kL for

This function produces a text file

This function produces an output windows showing the cost for each of the major categories.

This function produces an output windows showing costs for each of the major categories: rainwater tank, concrete base, pump (indoor), pump (outdoor), accessories, plumping cost, electrical costs and governement

irrigation during the day but irrigation would resume on the next day. (ii) For 1 to 7 days of consecutive rainfall, there would be no irrigation during the rainfall days plus none for the equal number of previous days of consecutive rainfall. (iii) For 8 to 21 days of consecutive

containing water savings achieved for a given tank size.

For a selected tank size, this function gives a BCR which considers the whole life cycle of the rainwater harvesting system.

File Open

Settings RWTAM

Water savings

Cost analysis Input

Annual Water Savings

Annual Water Savings

Yearly Water Savings

Benefit Cost Ratio (BCR)

Breakdown of Life Cycle Costs

Breakdown of Capital Cost

Rainwater Data File

of suburbs in Melbourne. A paper by Ming-Daw et al. (2009) focused on the development of a relationship between storage and deficit rates for rainwater harvesting systems. Results showed that as the deficit rate increased so too did the storage size of the tanks. Eroksuz and Rahman (2010) conducted research on the use of rainwater harvesting systems for multi-unit blocks in three cities of New South Wales (NSW), Australia. They found that in order to maximise water savings, larger tanks would be more appropriate and these tanks could provide significant water savings, even in dry years. A study in Brazil by Ghisi et al. (2009) aimed to assess the potential for potable water savings for car washing at petrol stations in the City of Brasilia found that an increase in the tank size enhanced the reliability of the rainwater tank notably in meeting demand. Kyoungjun and Chulsang (2009) showed that rainwater collection would only be feasible in South Korea during six months of the year. They also found that increased cost and marginal increase in reliability make larger tanks unsustainable. They also found that a benefit cost ratio higher than 20% could not be gained due to the low cost of water in South Korea. They suggested the cost of water supply would need to be increased by a factor of five for the rainwater harvesting system to become economically viable in South Korea.

There is often a lack of 'easy to use' computing tools which examine the viability of rainwater harvesting system in large buildings. The financial viability of a rainwater harvesting system depends on factors such as local rainfall, roof size, water demand, capital cost, interest rate, maintenance cost and mains water price. This chapter presents a computing tool that can be used to examine various scenarios of a rainwater harvesting system to compare water savings and financial benefits based on life cycle cost analysis. The first part of the chapter presents the computing tool followed by a case study illustrating the use of the computing tool and the associated results.
