Star Rating System
Simpson’s Water Quality 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.
| Quality | |
| 6-Star: Purer than Drinking Water Minimum levels of salts and trace chemicals. The treatment process includes several barriers for each pollutant. Usually includes two-stage membrane filtration including reverse osmosis, complemented by advanced oxidation and disinfection. Suitable for kidney dialysis, manufacture of pharmaceuticals and semi-conductors, boiler feed water and augmenting water supplies |
| 5-Star: Drinking Water Meets drinking water guidelines. The treatment process includes several barriers for each pollutant. Usually includes membrane filtration complemented by advanced oxidation and disinfection. Suitable for all urban uses and for augmenting water sources |
| 4-Star: Recycled Water – Open Access 3-Star recycled water which has is filtered and disinfected. Suitable for most non-potable urban, industrial and agricultural uses.May be used for residential gardens and toilet flushing but not bathing. May be used for irrigation of food crops that are eaten uncooked. May be used to augment water sources subject to limits on trace chemicals and dilution or environmental buffer rules. |
| 3-Star: Recycled Water – Controlled Access The treatment process removes nearly all organic matter by advanced biological processes. May also contain steps to remove phosphorus by biological means or chemical precipitation. After the biological processes the water is settled and disinfected. Suitable for discharge to rivers, lakes, estuaries and bathing waters. Suitable for most forms of irrigation subject to controls on access during spraying. Not suitable for food crops that are eaten uncooked |
| 2-Star: Treated Effluent The treatment process uses scavenging micro-organisms to break down organic carbon compounds biologically in the presence of air (also called secondary treatment). In the most common processes, air is pumped into a tank containing large number of scavengers in an activated sludge. Some processes also break down nitrogen compounds such as ammonia by varying the air supply. Needs supplementary settlement (clarification) and disinfection. Suitable for discharge to waters which have sufficient dilution and oxygen capacity. May be suitable for some land applications under controlled conditions. |
| 1-Star: Settled Wastewater The treatment process removes gross solids by screening and some biological solids by settlement in a tank (also called primary treatment) Not suitable for discharge or reuse (see Note 1). |
| No-Star: Untreated Wastewater |
The water quality descriptions in the star rating system are based on the premise of satisfying health and environmental protection requirements by treatment only so that recycled water is fit-for-purpose when it leaves the treatment plant.
(Note 1: In regions where high-technology treatment is not affordable, it may be possible to satisfy health requirements with lesser quality water by applying supplementary controls on application, harvesting and hygiene in line with the WHO Guidelines.)
The Asano Diagram
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. This extended version of the Asano Diagram includes the additional 5-Star and 6-Star water recycling options made feasible by new dual membrane and advanced oxidation processes.
Asano, T. et al (2007) Water reuse: issues, technologies and applications, McGraw-Hill New York, ISBN-13: 978-0-07-145927-3, p29
Simpson, J. (2006) Water Quality Star Rating – From Waste-d-water to Pure Water, Woombye, Queensland, Australia.
