A comparative study of greywater from domestic and public buildings C. Santos, C. Matos and F. Taveira-Pinto ABSTRACT Greywater (GW) can be an important resource for urban water consumption, replacing potable water for purposes that do not require drinking water quality. If applied on a large scale, this practice will reduce the potable water demand and the wastewater produced in urban areas, minimizing the negative impacts and costs of water extraction and wastewater treatment. A correct characterization of GW is important to assess its potential for a direct reuse or, if not possible, to make a correct definition of a feasible and cost-effective treatment system. This article aims to contribute to the characterization of GW produced in washbasins and showers in domestic and public buildings. A compilation of several works on GW collection and sampling produced by the authors is presented. Samples were taken from GW produced in showers and washbasins in households, changing rooms and in a restaurant. Results are compared with values presented in similar studies and compared with standards and guidelines published in different countries. C. Santos (corresponding author) F. Taveira-Pinto Department of Civil Engineering, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal E-mail: csantos@fe.up.pt C. Matos Engineering Department, Science and Technology School, University of Trás-os-Montes e Alto Douro, Quinta de Prados, apartado 1013, 5001-801 Vila Real, Portugal Key words | greywater, sustainability, water reuse INTRODUCTION Greywater (GW) is defined as wastewater from showers, baths, hand basins, laundry, washing machines and kitchen sinks. Many authors and guidelines around the world con- sider GW as wastewater only from showers, baths and hand basins, excluding the more contaminated water from washing machines and kitchen sinks. Compared to domestic wastewater, GW generally contains lower concentrations of organic pollutants and nutrients but a higher amount of sur- factants (Paris & Schlapp ). GW has the potential to be an important resource for urban water consumption since it can replace potable water in uses that do not require drink- ing water quality (such as irrigation and toilet flushing), reducing the demand on potable water supply. However, as Mandal et al. () point out, this is not the only benefit of this practice. GW reuse also conserves water resources for potable uses and decreases the amount of wastewater sent to the downstream wastewater infrastructure (including collection, treatment and disposal) and the negative impacts on the receiving environment. By reducing potable water consumption in urban areas, important economic savings can be achieved, not only for the population but also for governments. The inefficient use of water has not only negative consequences for the environment but it also represents higher energy use in treatment plants and supply systems, with extra financial and environmental costs (Santos & Taveira- Pinto ). As an example of potential economic and environ- mental benefits of GW reuse, three houses with GW systems were studied in England. The system collected GW from the bath and bathroom washbasins and then fil- tered and disinfected it. Treated water was then used to flush toilets. The potable water saved ranges from 24% in a family of seven persons, up to 65% in a family of three (EA ). On the other hand, in a small building with 30 inhabitants, almost 300 m 3 of potable water per year can be saved by reusing GW (about 30% of the total water con- sumption (Santos )). 135 © IWA Publishing 2014 Water Science & Technology: Water Supply | 14.1 | 2014 doi: 10.2166/ws.2013.181 Downloaded from https://iwaponline.com/ws/article-pdf/14/1/135/415354/135.pdf by guest on 08 June 2020