The cost of a litre of water is actually very low in Australia - which means that saving water by harvesting rain probably won’t save you a huge amount of water. That is, you won’t save a lot on your water usage charges.

However, collecting water in a tank can save you money in other ways:

• the amount of water you use form the mains is used to determine the amount of sewerage disposal you are charged. The assumption is that if you use more water, you will put more into the waste system, so reducing water usage will save you in sewerage costs
• a healthy garden can provide shading for your house which reduces your need for (and therefore the expense associated with ) air conditioning
• having water for growing your own fruit and vegetables will save you money from buying food at the shops - especially if you prefer organic options. It also is better for the environment as there is less transportation and farming machine costs.
• you can wash your car at home instead of at a commercial car wash - a much cheaper option!
• keeping soil around your home moist (by watering gardens) may prevent cracks in your house resulting from dried out soil and foundations. Fixing cracks in brickwork and plaster can be expensive and time consuming, and that doesn’t count re-stumping or potential dangers from instability either.