Liquid bounty

G Magazine (issue #21, July/August 2009)

Rainwater collection doesn’t have to be limited to the water flowing into your tank from the roof.

Rain Produce

Wonderful produce - all grown with rainwater!

Credit: Brad Lancaster

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The US desert city where I live – Tucson, Arizona – receives just 304 mm of rain on average each year. That’s nearly half the amount of rain that falls on Australia’s driest city, Adelaide.

Like many communities around the world, Tucson fails to see the rain as an asset, letting rainwater run off into storm drains and sewers, while pulling from the water table faster than nature can replenish it. In Australia, this practice has resulted in water restrictions in major cities and depletions of the water table as severe as 80 per cent in many areas. In Tucson, the same practice has dried up countless springs and wells, along with the Santa Cruz River, which once ran perennially through the west side of town.

But it doesn’t have to be this way. Rather than using half of our most expensive and valuable water to irrigate the landscape, as the typical single-family residence in both Australia and the US does, we can use harvested on-site rainwater on our properties instead.

At my own house (home to three adults and a baby) we use less than 75,000 litres of municipal water and harvest some 379,000 litres of rain each year. Some of this is captured from the roof run-off in a 4,500-litre ferro-cement tank, but the bulk is harvested in the soil with earthworks – simple basins, terraces, contour berms and check dams – which also collect greywater when the rain isn’t around. They cost little more than the price of a shovel. Together, the harvested rainwater and greywater cover over 98 per cent of our landscape water needs. Even better, no mechanical pumps are needed. Instead, living ‘pumps’ of vegetation thrive off the harvested water, offering shade, fruit, wildlife habitat, erosion control, windbreaks and beauty in return. We also grow much of our household food in an organic garden using the collected water.

Desert oasis

My brother Rodd and I started working with rainwater harvesting in 1994. Both self-employed at the time, earning what the US government considers poverty wages, we had pooled our resources to buy a home – a decrepit little house on a 0.05-hectare lot.

Aside from the about-to-be-condemned house, a shed and a couple of dying trees, the lot itself was dry, flat and barren, like many of the properties in the neighbourhood back then.

But using a range of earthworks, we dramatically re-shaped our yard to capture the rain and nurture the growth of plants and trees. Fifteen years later, our property value has shot through the roof. We now live in an oasis in the desert, with summer temperatures averaging 5.5°C lower than in our neighbours’ yards. Our utility bills have also dropped steadily since we moved in – in fact, we’ve reduced our water bill so much that
the City Water Department has visited us four times, wondering whether our meter was broken!

For the newcomer, all of this might sound complicated. But in the course of creating our sustainable oasis, my brother and I arrived at eight basic principles that anyone can use to implement a successful water-harvesting strategy of their own:

1. Begin with extended, thoughtful observation of your property

During the first rainfall after we bought our property, Rodd and I watched where the water pooled against the house and how the bulk of the rain ran off our site into the street. We also noticed things like noise, lights and fumes from the street, and where patches of excessive sun and shade fell. This helped us decide where to plant vegetation to buffer noise and light pollution, create privacy screens, provide summer shade and let in winter sun – and where we would be planting with a mind for the vegetation to depend entirely (or at least primarily) on rainwater.

Next, we calculated the rainwater resources available within our site’s ‘watershed’. For us, this area included not only what fell on our property, but also what fell in the six-metre wide public area adjoining the property: the section of street draining past the pathway, and, with permission, even the run-off from our neighbour’s roof. This totalled an estimated availability of 397,000 litres of rainwater in an average year!

2. Work with gravity

Start harvesting rain at the top of your watershed and work your way down. The top of your watershed is its highest point – in most cases the roof of your house. Take a look at it. Where do the gutters drain? Where is rainfall currently being directed? This is where you should begin, with mulched water-harvesting basins and plantings (at least three metres from the building’s foundation). On our property, just under half of the roof run-off is directed to earthworks and fruit trees north of the house. The rest is directed to our above-ground tank, which sits on an elevated platform, allowing gravity to work in our favour by circulating water from the roof’s gutter to the tank and from the tank to the garden. Whatever type of tank you choose, having your garden nearby will negate the need for a long hose, which results in a loss of water pressure. It also makes watering more convenient.

3. Plan an overflow route & manage it as a resource

Eventually, all water-harvesting systems will be faced with a storm that exceeds their capacity. For this reason, all rainwater harvesting structures should be planned and managed so that the system can overflow in a beneficial way.

Overflow from our backyard tank is not directed straight to the storm drain. We plant that overflow in the soil via a series of adjoining mulched basins that passively irrigate a citrus tree and our garden. Additionally, all of our sunken earthworks have an overflow ‘spillway’. Typically, one earthwork overflows to another, and that to another, until all are full and then, if needed, the lowest earthwork can overflow to a natural drainage or stormwater drain.

4. Start with small & simple strategies that harvest rain close to where it falls

The water-harvesting earthworks Rodd and I created were so simple, but highly effective. We dug level-bottomed basins, or ‘rain gardens’, and applied a 10-cm thick layer of surface mulch within them in order to soak up rainfall and run-off throughout our watershed – once again starting at the highest points of the yard and working down.

Sloped sites could use contour berms, swales and terraces. In highly urbanised sites you could replace impervious pavement with porous pavement, install a living ‘green roof’, or get rid of paved surfaces altogether.

5. Spread, slow & infiltrate the flow of water into the soil

Slowing, spreading and sinking the water on your property increases soil-water contact, calms the flow and prevents erosion and downstream flooding.

Raised pathways and gathering areas are also a great strategy for spreading water through the landscape. This pattern of high and dry regions that drain to adjoining basins kept sunken and moist will help to define those areas through vegetation while spreading and sinking the flow of water.

6. Maximise living & organic groundcover

All your basins and other water-harvesting earthworks should be well mulched and planted, primarily with perennials, to ensure living roots year after year. This produces the ‘living sponge’ effect that will create food and beauty in your surrounding landscape. As plants grow, a vast network of growing roots and beneficial micro-organisms in turn improves the soil’s ability to infiltrate and hold water.

Groundcover is equally important for mosquito control. Water-harvesting earthworks with a living sponge allow water to quickly infiltrate below the surface of the soil (typically within one hour) so it won’t puddle and create the standing water that mosquitoes need to hatch. It also ensures that a minimum of water is lost to evaporation.
To determine what to plant in or near your earthworks, go for a walk in the natural, unmanaged areas near your home. Out in the wild, you’ll notice which plants grow naturally in depressions – plant the same ones in your water-harvesting basins. Then plant native vegetation that prefers better drainage beside (but not within) your earthworks. In general, for a low-maintenance, highly successful home landscape, native plants are the best choice since they are the best adapted to the local climate, soils, and wildlife.

7. Maximise beneficial relationships and efficiency by ‘stacking functions’

Water-harvesting strategies offer maximum benefits when they’re integrated into a comprehensive overall site plan. We focussed on locating the earthworks where we could stack functions with multi-use vegetation. In other words, we considered where we wanted food, privacy and shade, and planted accordingly.

One of the nicest features along our property line is a living fence of native plants that creates a suntrap which shades our garden from the afternoon sun, forms stormwater control, and enhances habitat for native songbirds and butterflies.

8. Be prepared to continually reassess & improve your system

Five years ago, Rodd and I rerouted our bathtub, shower and bathroom sink plumbing to passively irrigate the rain gardens beside our fruit trees with greywater. Rain irrigates them when it falls and greywater irrigates them when the weather is dry.

As a result, our fruit production has soared. In addition, we reduced our yard’s impermeable hardscape by parking on the street and replacing the asphalt driveway with earthworks and, of course, more vegetation. We also succeeded in implementing a Water Sensitive Urban Design (WSUD) system that gathers street run-off into kerbside mulched basins to grow a green belt of trees along the street and footpath.

Since we started working on our property 15 years ago, our passion for rainwater harvesting has caught on, with many neighbours implementing similar systems. Our neighbourhood today – once characterised by dry, dusty yards – is one of the greenest and most liveable areas of the city.

My advice to anyone who wants to start living more sustainably is to take the first step with harvesting the rain. Start at the top. Start small. But above all – start!

BRAD LANCASTER is a permaculture expert and consultant based in Tucson, Arizona.
His award-winning books Rain Harvesting for Drylands and Beyond, Volumes I and II
are available through his website www.harvestingrainwater.com and through Tower Books in Australia (www.towerbooks.com.au).