Storing rainwater makes sense for commercial properties as well as residential homes. The issue is acute for Bunnings, which as a big corporate player wants not only to do the right thing - it is a significant seller of water-saving products - but is also a big user of water through its nurseries.
Company veteran John McGregor was asked to tackle the issue a couple of years ago. ”We made a conscious effort to reduce carbon dioxide output and water use,” said Mr McGregor, now in charge of sustainability at Bunnings.
”We found it could also have an impact on the costs of the business. That was not our focus, but an offshoot - the water and electricity price increases were not seen until two years ago.”
His starting point was that a typical Bunnings warehouse has 8000 square metres of roof area - and so the company began retrofitting rainwater tanks at all its stores.
”Consultants did a study of east-coast rainfall averages, and at the same time we measured our water consumption,” Mr McGregor said. ”The main use was irrigation of plants and nurseries and flushing toilets.
”The typical storage capacity required for each Bunnings store was 70,000 litres. This became the model for water usage.”
”Our calculations showed that we used 8000 litres just when we turned on sprinklers,” Mr McGregor said, although he added that water use could not be monitored as closely as energy. Potable water is still obtained from town water supplies.
It took three years to implement the program in Australia. ”We spent $7 million in total. Each installation cost about $55-$60,000, including the cost of tanks and the installation,” Mr McGregor said.
The drought played havoc with the program, but Bunnings found that it needed water from only 20 per cent of a typical roof. ”We designed a simple system, cutting into downpipes at strategic locations. We took water from a side closest to the nurseries - about 1000 square metres of roof was sufficient for us to maintain the program,” he said.
New stores, such as that at Pakenham, south-east of Melbourne, have been fitted with underground storage tanks. ”Pakenham has 40,000 litres underground, and a 5000-litre tank that takes the water off the car park,” Mr McGregor said. ”It has an element of contamination, so is not used on seedlings. We use it to irrigate the external landscapes and hardier plants.” Local councils have been keen for Bunnings to use the water that falls on car parks.
The program has had a dramatic impact on water consumption. ”A lot of the water from our sprinkler systems fell on to the concrete floors, so the company instigated hand-watering twice a day, which used about 1100 litres per day, depending on the size of the nursery,” Mr McGregor said. ”That comes with extra wage costs, but we are prepared to wear that.
Hand watering draws just from the tanks, which fill only from roof rain, never from the town supply. ”Under normal circumstances, we can be 80 per cent self-sustaining in water, but that still depends on average rains,” Mr McGregor says. ”It’s not rocket science - but a simple, effective way of using water.”
All sorts of schemes were put to Bunnings as methods to save its excess water. These ranged from pumping the water into a small trailer with a tank, paying for the water, and then returning the trailer and tank to Bunnings. ”We could not make it work,” Mr McGregor said.
In another, a local council wanted to use any spare capacity to water protected red gums. ”Nothing came of that - and now it has rained.” Another idea was to relocate tank water to an aquifer to be stored until it was needed, but this idea was abandoned due to the risk of contamination.
”Using the remaining 80 per cent of our water would require a lot of infrastructure. But we would be happy to donate it if someone shared the cost of storing and harvesting,” Mr McGregor said.
