Amy St Lawrence standing next to her rain garden. (Hamish Dunlop)
By Hamish Dunlop
Planetary Health Initiative writer Hamish Dunlop talks to Amy St Lawrence from Blue Mountains City Council’s Healthy Waterways Team. Amy explains what she’s doing at her home to collect and use water. She also talks about how her rain garden reduces run-off during and after rainfall.
Rain, Rain and Storm Water Drains
La Niña rains have caused flooding and infrastructure havoc over the last few years. We’ve had a serious dose of it in the Blue Mountains. I knew it was getting bad when the NRMA started sending notifications on my phone saying potholes beware. I feel lucky not to have driven through knee deep water and found myself with a burst tyre or worse. Many of us were left asking the questions: “Why is this street more like a gushing creek?” and “Is there anything we can do to reduce this amount of water?”
One of the things Blue Mountains City Council is doing to manage stormwater is building rain gardens that act as biofiltration systems. This makes a big difference at urban planning and sub-catchment retrofitting levels. But stormwater management reaches all the way from the house to the catchment. Just like keeping plastic bags out of landfill one bag at a time, there are things we can all do to help mitigate stormwater effects.
Banksia Street rain garden above Wentworth Falls Lake. (Blue Mountains City Council)
Amy St Lawrence is the Aquatic Systems Officer with Blue Mountains City Council’s Healthy Waterways Team. She’s invited me to her home to see how water is managed on her property. “Urban development has drastically affected how water moves through the landscape. Stormwater can damage our endangered swamps. This happens through the processes of channelisation, nutrient enrichment, weed seeds and pollutants entering our waterways.”
Amy wants to ‘practice what she preaches’. This means managing runoff, but also using the stored rainwater. The tank is plumbed into her house’s hot water system, toilets, washing machine and external taps. A rain garden captures and filters water too.
Amy’s rain garden. (Hamish Dunlop)
Amy’s rain garden is below her back porch. She points out the down pipes that carry water from the roof into the garden. The water garden is lined, like a pond, because it’s close to the house.
A rain garden or biofilter consists of vegetation on top. All the plants are native and well suited to the sandy, low nutrient substrate. Amy planted ferns and a few scattered tea trees because the garden is in a shady spot. She planted flax lilies, Gahnia sedges and button grass in the corner which gets more sun.
The plants grow in the sand-based filtering medium with gravel at the bottom. The sand and gravel layers are 40 cm and 15 cm deep, respectively. An overflow inlet sits around 8 cm above the sand. Water can fill the garden, as if it was a pond, and then slowly get absorbed.
In the event of a torrential downpour, excess water that reaches the overflow inlet, flows away from Amy’s house into an infiltration pit. In the absence of an infiltration system, rain garden overflow can often be directed into the stormwater system. Whether you have an infiltration system or not, rain gardens play a positive role in managing the water on your property. They reduce how much and how quickly water enters our World Heritage Area, limiting the damage to the natural environment.
Other than controlling flow, rain gardens filter the water. They can address pollutants including sediment, excess nitrogen and phosphorus, heavy metals, pathogens like coliform bacteria and micro pollutants including pesticides. It’s amazing what sand and plants can do. Filtering is facilitated by the physical properties of the sandy medium. The plants absorb pollutants and their roots support a variety of microorganisms that filter out pollutants.
If you’re keen to have a go at making your own rain garden, there are good resources online. Melbourne Water provides instruction sheets with information and diagrams on how different kinds of home rain gardens are constructed: https://www.melbournewater.com.au/water-and-environment/saving-water/raingardens
Illustration from one of Melbourne Water’s instruction sheets on building rain gardens. (Melbourne Water)
The water tank Amy and her partner bought. (Hamish Dunlop)
Recognising what a precious resource water is, Amy and her partner installed a water tank and had it plumbed it into their house to feed the hot water system, toilets, washing machine and external taps. They sourced it from a company that makes them to specific dimensions. At 7000 litres, it required a concrete rather than gravel base. They jumped into the project headfirst, buying the tank before engaging a plumber. Amy says it would have made more sense to find a plumber first and discuss their specific household requirements.
Amy’s water tank is plumbed into the hot water heat pump that supplies her family with hot water. (Hamish Dunlop)
Hot water comes from the tank-fed heat pump while drinking water comes directly from the mains supply. Amy realised the hot water pump had to be tank-fed to make best use of the stored water and create space for rain. She says her family goes through a tank quite quickly, mostly for showers. Toilet flushing and laundry are not insignificant though. Energy Star washing machines use around 50 litres per load. Single flush toilets use between nine and eleven litres. An average bath uses around 80 litres and a four-minute shower with a standard head uses approximately 36 litres. It all adds up.
The pump attached to the water tank. (Hamish Dunlop)
The average Australian home has a roof area of 180m2. This means that 10 mm of rainfall can harvest 1800 litres of water. The Bureau of Meteorology calculated that between 1500-1600 mm of rain fell on the Blue Mountains in 2021 and 2022. Even if we only get 600 mm of rain this year, that still equates to 108,000 litres. While rainfall varies across the seasons, this averages 9000 litres a month.
This gauge indicates how full the tank is. When it gets low, Amy switches the house supply back to mains water. (Hamish Dunlop)
I asked Amy about how much she thought her mains water usage had gone down since installing the tank. She calculated they reduced their mains water consumption by 74% based on the 5 quarters before and after the installation. Across a year, this equates to an average saving of 141,000 litres! However, Amy points out that because water is undervalued economically, the saving is only $350 a year.
The total cost of the project was slightly over $6000. Half of this was for the tank and pump. The other half was for the plumbing, all the connections and the new stormwater lines from the roof. This means that financially, the project would pay for itself after 20 years.
Amy acknowledges that to get the financial return makes a tank system a long-term investment. But for her, it’s not just about economics. “I get an unquantifiable amount of satisfaction every time I have a shower that is fed by our own roof water – transforming an urban runoff problem to a precious resource via a simple tank and pump.”
This story has been produced as part of a Bioregional Collaboration for Planetary Health and is supported by the Disaster Risk Reduction Fund (DRRF). The DRRF is jointly funded by the Australian and New South Wales governments.