Can domestic bores help save our drinking water?

Too much of our drinking water is still being used to water Perth gardens, according to CSIRO's Dr Tony Smith.

One suggested solution to the problem of dwindling water supply was to increase the number of garden bores in Perth's suburbs, but given Perth's drying climate there is a doubt as to whether this is sustainable.

"Perth people know all about domestic bores because about a third of all gardens use groundwater from the shallow sandy aquifer," Smith said.

"However, millions of litres of drinking water are still being used to keep lawns and gardens green."

Smith says Perth's groundwater supply is facing some serious threats, and that good data is essential to understand the resource and manage it wisely.

"More than 80% of all the water used in Perth comes from groundwater," Smith said.

"Less than 20% now comes from the hills catchment, which historically was Perth's main water supply. Around 45% of the total water supply is treated to drinking water quality but it's not all used for drinking.

"Encouraging more garden bores is one way to preserve precious scheme water for drinking uses. However, we need to know how many bores the aquifer can support without unacceptable impacts on groundwater dependent ecosystems and other uses such as public open space. About 16,000 rebates have been issued for drilling bores since February 2003, equivalent to around 14 bores per day."

Smith said the biggest threats to Perth's groundwater are seawater incursion into the aquifer, the loss of valuable wetlands, and soil and groundwater acidification.

"The research team used data from the past 10 years, and looked at what they termed freshwater "thickness' at 543 sites in the Superficial Aquifer."

Smith's team examined more than 500 monitoring bore records in the greater Perth region. It concluded that there were some suburbs where increasing the number of bores could lead to less drinking water being used on domestic gardens.

The study also identified suburbs where increased extraction would not be viable if the current rate of water table decline continued. In these areas, more bores would only be possible if they, and the declining levels, were offset by more efficient use of the water by current bore owners.