The facts about greywater use in sewered areas

23 February 2006

The facts about greywater use in sewered areas

The use of greywater in Toowoomba’s sewered areas comes with long-term problems.

Toowoomba City Council was faced with four options when deciding whether or not to accept applications for greywater use facilities in sewered areas, this week.

The options Council looked at were:
· allowing the full use of greywater,
· allowing the use of laundry greywater only,
· allowing the use of non-laundry greywater only and
· not allowing the use of greywater.

Officers from Toowoomba City Council’s engineering, planning and plumbing sections recommended that Council not accept applications for greywater use facilities in sewered areas at this time.  Bucketing of greywater is permitted, with the exception of kitchen greywater.

Strategy and Governance portfolio chair Cr Lyle Shelton said state government legislation was changed, allowing local authorities to permit use of greywater within sewered areas from 1 March 2006 if it was environmentally sound. Previously all wastewater was required to be discharged to sewer.

The potential impact of laundry greywater on soils, the difficulty of meeting the requirements of the Act on an average sized housing block, expected costs of greywater use facilities and the extra resources needed to administer applications and licenses were major concerns listed in the officers’ report.

Environment and Heritage portfolio chair Cr Sue Englart referred to a National Centre for Engineering in Agriculture (NCEA) study commissioned by Toowoomba City Council last year that rang alarm bells.

The study found laundry greywater – the largest component of greywater - contained concentrations of nutrients (nitrogen and phosphorous) and soluble salts which, if applied to Toowoomba soils over long periods of time, could result in soil degradation, increased soil pH and poor plant growth of those plants adapted to acidic conditions.

Under the Plumbing and Drainage Act, greywater is defined as domestic wastewater from a bath, basin, kitchen, laundry or shower, whether or not the wastewater is contaminated with human waste.

However, a subsequent amendment to the legislation prohibits the discharge of kitchen greywater to a greywater diversion device or treatment plant.  Kitchen greywater would have to discharge to the sewer if the changes were allowed.

A greywater use facility consists of a greywater diversion device, or treatment plant, and a greywater application area. The greywater treatment plant or diversion device must be installed on the premises for treating greywater that is generated on the premises.

Greywater disposal must be a minimum of 100mm below ground into soil in grassed or other suitably vegetated area.

Cr Englart said the laundry water component of greywater had the potential to seriously impact on Toowoomba’s soils. The NCEA study concentrated on laundry greywater as it normally represented the largest proportion of household greywater.

“These concerns could only be put to rest if the sodium content of laundry detergents was strictly controlled and that would only happen if there were measures taken on a national level to reduce the sodium content.”

Cr Englart also highlighted problems with greywater discharge to already saturated soils during wet weather.

“If heavy rainfall occurs there is the possibility of overland flows of stormwater contaminated with greywater.  This could have health and amenity impacts in areas such as parks and footpaths and in the disposal area itself,” Cr Englart said.

Cr Shelton said if Council had approved the use of greywater in sewered areas, applicants would have faced costs of thousands of dollars for design, approval and correct installation of the diversion or filtration device.

The lot size and setbacks (distance required between disposal points and other infrastructure) would make many residential properties in Toowoomba unsuitable for installation of a greywater use facility.  Setbacks are the minimum distances required between where the greywater is applied and infrastructure such as dwellings, property boundaries, retaining walls, and swimming pools.

“Most sites of less than 1000 square metres would be unsuitable for greywater use,” Cr Shelton said.

“In the event that greywater use was permitted in sewered areas, Building Codes Queensland had advised larger setback distances would be required in areas of highly reactive soils.”