Greywater irrigation options for treated and untreated systems

Untreated greywater distribution

Distribution of untreated greywater can be through 4 types of irrigation systems:

Sub-soil irrigation/drainage

This practice is not recommended. Greywater is distributed by gravity through trenches dug into the ground. This method is usually associated with septic systems and water disposal rather than beneficial use. There are a number of variations that rely upon absorption and/or transpiration of the greywater. This type of irrigation is not recommended as it is generally not good irrigation practice and not the most efficient use of the water unless deep rooted plants are watered.

Sub-surface irrigation

This system is usually pressured and installed between 100mm below the ground, usually in grassed areas. The untreated greywater is distributed through small-diameter perforated pipes or dripper lines and applied directly to the root zone at a control rate so that the plants can utilise the water. Adequate filtration is required to ensure pipe perforation or drip holes are not clogged with suspended solids in the untreated greywater.

Gravity irrigation systems rely on gravity to evenly distribute the greywater to all parts of the irrigation area. Gravity irrigation systems should only be installed in flat/gentle slope sites, to avoid ponding of greywater at the lowest points in the irrigation area. Check with the manufacturer for recommended pipe diameters and maximum irrigation pipe work lengths. The key to good irrigation practice is to maintain distribution uniformity across the irrigation area.

Subsurface pressurised irrigation systems are ideal for sloping sites, as these systems can evenly distribute the greywater across the irrigation area. Check with the manufacturer for recommended pipe diameters and pump pressure requirements as items will vary depending on the irrigation pipework design, length and overall irrigation area as to the size required.

Gravity Feed Irrigation System

Gravity feed, low pressure irrigation system. Note even distribution and no pooling of water at low point. Source: Standards Australia and National Water Commission.

Covered surface drip irrigation

This enables untreated greywater to be applied directly to the surface of the soil under a layer of mulch. The greywater is distributed under pressure from small diameter perforated pipes or dripper lines. This system is usually applied to plants such as, fruit trees and grape vines.

Manual bucketing

Manually irrigating with greywater using a bucket (e.g. collecting shower and laundry water for reuse) enables reuse of small quantities of untreated greywater. This should not be done during wet weather conditions.

Treated greywater distribution

The type of greywater irrigation system that can be installed will depend on the greywater quality and the site to be irrigated. The irrigation system associated with the Greywater Treatment System does not require accreditation by state authorities, however, does require prior local council approval of design and maintenance agreement.

When designing a greywater irrigation system it should be capable of supplying sufficient greywater to meet the highest daily demands of the garden, or for additional water to be applied from non-greywater sources in a supplementary irrigation system.

Distribution of treated greywater can be through 5 major types of irrigation systems dependent on the level of treatment:

Sub-soil irrigation/drainage

This not recommended. Greywater is distributed by gravity through trenches dug into the ground. This method is usually associated with septic systems and there are a number of variations that rely upon absorption and/or transpiration of the greywater with limited control of water release to match plant requirements. This is not considered an efficient irrigation method for beneficial use of greywater and therefore not recommend unless deep rooted plants are irrigated to match demand.

Sub-surface irrigation

This system is usually pressured and installed 100 mm below the ground. The greywater is distributed through small-diameter perforated pipes or dripper lines and applied directly to the root zone at rates required by the plants so that the plants can utilise the water without excessive runoff or leaching.

Covered surface drip irrigation

This enables greywater to be applied directly to the surface of the soil under a layer of mulch. The greywater is distributed under pressure from small diameter perforated pipes or dripper lines at rates required by the plants.

Surface irrigation

Exposed dripper is one form of surface irrigation.

Surface irrigation can be used for relative level areas and the greywater usually needs to be treated to a high quality before it can be used for spray irrigation. Check with the manufacturer for recommended pipe diameters and pump pressure requirements as items will vary depending on the irrigation pipe work design, length and overall irrigation area as to the size required.

Pressurised irrigation system

Pressurised surface irrigation of greywater - only suitable for treated greywater systems. Check with the responsible regulatory authority as to the level of treatment and setback required by the greywater. Source: Standards Australia and National Water Commission.

Spray irrigation systems

These systems are not recommended as they increase the risk of exposure to people. If spray irrigation is used the greywater needs to be treated to a higher level to ensure this risk is minimised. The greywater is distributed under pressure through surface spray devices that should maximize droplet sizes, throw and plume height to minimize water loss through evaporation and maximize plant use of the greywater.

Discover more about using greywater: