Simple Greywater Garden Design

greywater-design

Only three per cent of the earth’s water is fresh water; and only one per cent of this can be used for life, people included.

While the amount of water cycling on earth remains the same, the availability of this water – for humans – depends on where it is and how we use it. Water cycling through land-based soil and plant systems returns to the land via the atmosphere and rainfall within a few months. Whereas water flushed down the drain and out to sea takes hundreds of years to cycle through the ocean to the atmosphere and fall again as rain!

Human systems generally spoil water quality, then flush it from land to sea quickly. A better solution would be to re-use ‘waste’ water, locally. Imagine a landscape of abundant, biodiverse and beautiful gardens that capture and store greywater, break down pollutants, absorb nutrients, replenish groundwater and re-humidify the atmosphere, supporting regional rainfall patterns and water cycles.

One way to achieve this is with a simple, easy-to-install greywater system for your garden. Such systems are lowtech, low-energy, low-cost, easy to maintain and they also:

  • reduce household fresh water consumption
  • eliminate harmful chemical inputs
  • return used water to the land
  • protect and build soil structure and organic life in the soil
  • capture and cycle water and nutrients through soils and plants
  • grow abundant, biodiverse and beautiful landscapes.

Greywater Analysis

The quality and quantity of household wastewater varies depending on the source, so it makes good design sense to keep each source separate in a greywater system. The main sources are bathroom, kitchen sink, dishwasher and laundry.

Firstly you will need to identify:

  • the amount of water going through the system
  • the amount and type of solids
  • sodium, phosphorus and pH levels
  • pathogenic bacteria levels
  • temperature.

Bathroom is the highest quality and largest volume. Solid particles include dirt, hair and lint. Soaps and shampoos are low in sodium and phosphorus. Pathogenic bacteria and temperature low.

Laundry is potentially the worst. Steer clear of powdered detergents. Nappies, although high in pathogenic bacteria, can be managed by soil and microbes. Lint and soil are the main solids and temperatures generally low.

The kitchen sink is a great source on all fronts except for solids – food scraps, grease and oils – and boiling water. A biological filter is needed here and behaviour changes at the sink, both of which need due diligence!

Finally the dishwasher, probably the worst, due to dependence on powdered detergent and high temperature discharges.

Detergents

The chemical composition of detergents is the main threat to soil and plant health in greywater systems, so it is important to use the right sort. Sodium, pH and phosphorus levels of detergent are the main concerns. High levels of sodium collapse soil structure and raise salinity. High pH detergents increase soil pH, which blocks the availability of minerals and nutrients to plants. Phosphorus, an essential plant nutrient, used in detergents can leach into and degrade waterways. Powdered detergents are generally very high pH, high in sodium and phosphorus. So use a liquid detergent which is low in these elements.

Consider starting your system with bathroom wastewater, as it is the highest quality and largest volume.

Below: Bathroom greywater diversion device (GGD);
Right: Greywater garden.

greywater-design
greywater-design

SETTING UP THE SYSTEM: DIVERTING THE GREYWATER: The greywater diversion device (GDD)

Once the greywater leaves the house, it needs to go into a greywater diversion device (GDD). This catches solid particles so that they don’t block the distribution pipes, and can direct it to different areas of the garden.

There are two types of GDD, a coarse-solids GDD for laundry and bathroom, and a food-waste GDD for the kitchen sink and dishwasher that incorporates a worm farm. Here we will focus on how to create one for the bathroom.

The main parts are:

  • 25 litre rigid plastic vessel – made from a 300 mm square stormwater-pit box, or recycle the base of an olive drum, the GDD
  • shadecloth or flywire, wrapped around wire mesh
  • tray with leaf-litter
  • 25 mm threaded barbed tank outlets
  • 25 mm barbed inline valve, to isolate distribution lines
  • 25 mm LDPE flexible distribution line
  • 10 litre plastic vessel.

Start by covering the 25 ltr plastic vessel with wire mesh wrapped in shade cloth or flywire to keep insects out. A tray filled with leaf-litter is placed on top, at the wastewater inflow, to filter out any solids like hair and lint. Divert the outlet pipe from the house over the leaf litter so that all water runs through it.

Split the volume. Thread the barbed tank outlets in the base of the plastic vessel to split and spread the volume to separate gardens. Make sure you put them as close to the bottom as possible, so that you don’t have stagnant water sitting beneath them. As an example, a four-person household, using around 200 litres a day, would need four outlets.

From each outlet connect a distribution line long enough to reach the garden, with a valve in an easy-to-access spot to enable you to control flow. Place the valve close to the GDD so that water doesn’t sit in the lines and go septic.

The Greywater Garden

Once the GDD and distribution lines are in place, it’s time to create your gardens.

Start with the earthworks. Create a small basin 1500 mm in diameter and 300 mm deep. Create a mound around the basin to contain the wastewater. In high rainfall areas it’s important to prevent surface water runoff from flooding the greywater basin, but in arid regions surface water runoff can flood the basin to help flush sodium build-up out of the soil.

To keep the end of the distribution line clear from blockage, insert it through a ten litre plastic vessel with the base cut off. Place a simple cover over the container and place in the basin.

Backfill the basin with woodchip. This creates an environment suitable for the decomposers which convert solid and soluble organic matter in the greywater to a form available for plants to thrive.

Now its time to plant out your water-loving plants.

Planting

Plants are the pumps of the system: transpiring wastewater back to the atmosphere; holding back salt-laden rising water tables; catching and converting phosphorus into biomass; maintaining soil structure and pore space.

The basin and mound earthworks create a range of soil depths and drainage. This is important because not all moisture-loving plants like wet feet. Position plants to suit their preference for drainage, for example place citrus on top of the mound and waterloving comfrey at the basin edge.

Select plants for:

  • high irrigation demand all year round
  • ability to survive phosphorus accumulation in sandy soils
  • growth habit, for stacking – ground cover, herb, grass, shrub, understorey, canopy, vine, leguminous
  • growth rate, for succession – fast and slow
  • root system – surface and deep fibrous, tap and spreading.

Selection of plants also depends on climate. In low-frost/ no-frost areas this could include:

  • ground cover, such as sweet potato
  • ground herbs, such as comfrey and arrowroot
  • shallow rooted grasses, such as Lomandra species and lemongrass
  • deep rooted grasses, such as bana grass and clumping bamboo
  • small shrubs, such as salvia and cassava
  • tall herb, such as banana
  • leguminous shrub such as acacia and pigeon pea
  • canopy fruit/nut trees, such as macadamia.

Now you just have to jump in the shower and test it out. No more wasting water down the drain, and no more using drinking water for watering your garden!

Dan Deighton is a permaculture designer, teacher and consultant and with Aaron Sorrenson runs Elemental Permaculture. www.elementalpermaculture.wordpress.com

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