Recycled Water Quality
Water should be judged on its quality, not its history.
Dr Louis Van Vuuren,
Matching recycled water quality to beneficial uses requires an understanding of health and environmental requirements. Measures to achieve appropriate recycled water quality are determined firstly by treatment. The degree of treatment depends in part on the source and the hydraulic and biochemical characters of the wastewater. Overall recycled water outcomes may also be controlled by how recycled water is distributed and handled. Risk assessment and system management measures may improve outcomes.
Protection of Public Health
Since 1854 when John Snow identified wastewater contamination of the Broad Street pump as the cause of a cholera outbreak in London, preventing pollution of drinking water sources has been a fundamental tenet of public health protection. The subsequent development of sewerage systems to remove and treat wastewater and the provision of reticulated water supplies delivering filtered and chlorinated water has greatly reduced the incidence of infectious diseases in society. The provision of reticulated water and sewerage systems in cities in the late 19th century and early 20th century reduced the incidence of infectious diseases by a factor of ten and halved the death rate.
Untreated wastewater typically contains a variety of biological and chemical constituents that may be hazardous to human health and harmful to the environment. The aim of wastewater treatment is to remove harmful constituents down to levels which allow the treated water to be safely discharged to the environment or to be recycled for beneficial uses.
Depending on the level of treatment, recycled water may contain residual levels of micro-organisms such as bacteria, viruses or protozoa which pose infection if ingested. It may also contain residual levels of chemicals which could be harmful to health if ingested in large quantities.
Water recycling systems need to be designed to ensure that use of recycled water is such that operators or the public are not exposed to significant risk of infectious disease through contact with or ingestion of recycled water.
In most countries, the authorities have now developed regulations or guidelines for recycled water systems. When recycled water is treated and applied to a beneficial use as prescribed, the risk of infection is negligible.
Protection of the Environment
Recycled water generally contains higher levels of salts and plant nutrients than freshwater. Water recycling systems need to be designed to ensure that the salts and plant nutrients do not cause adverse impacts on soils or surface water and groundwater systems. It is also necessary to ensure that residual chemical levels are below the levels which might have toxic effects on soils or plants.
Health Studies and Risk Assessment
It is common to undertake quantitative risk assessments for a water recycling application to assess the public health risks arising from exposure to recycled water.
Quantitative microbial risk assessment of infection risk involves assessment of exposure, dose and response. Risk management strategies to reduce infection risk may include steps to reduce exposure or reduce the dose. Measures may include treatment, distribution, application, handling or hygiene controls.
Detailed health studies have been carried for some projects where use high grade recycled water to augment drinking water supplies has been proposed.
The Star Rating System
Simpson (2006) has developed a Star Rating system for Water Quality. The following table differs from Simpson’s original descriptions. The main change is a change in the description of 3-Star Water to “Recycled Water” because water of this grade is suitable for a wide range of beneficial uses.
| Rating | Quality |
| 6-Star | Purer than Drinking Water |
| 5-Star | Drinking Water |
| 4-Star | Recycled Water – Open Access |
| 3-Star | Recycled Water – Controlled Access |
| 2-Star | Treated Effluent |
| 1-Star | Settled Wastewater |
| No Star | Untreated Wastewater |
There is a more detailed description in the Star Rating Article.
The Simpson Star Rating System can be combined with the Asano Diagram to give an overall picture of the place of water recycling in the urban water cycle.
