text: In an unsustainable system there is insufficient maintenance of the water networks, especially in the major pipe lines in urban areas. The system deteriorates and then needs rehabilitation or renewal.
  Householders and sewage treatment plants can both make the water supply networks more efficient and sustainable. Major improvements in eco-efficiency are gained through systematic separation of rainfall and wastewater. Membrane technology can be used for recycling wastewater.
  The municipal government can develop a “Municipal Water Reuse System” which is a current approach to manage the rainwater. It applies a water reuse scheme for treated wastewater, on a municipal scale, to provide non-potable water for industry, household and municipal uses. This technology consists in separating the urine fraction of sanitary wastewater, and collecting it for recycling its nutrients. The feces and graywater fraction is collected, together with organic wastes from the households, using a gravity sewer system, continuously flushed with non-potable water. The water is treated anaerobically and the biogas is used for energy production.
  The sustainable water supply system is an integrated system including water intake, water utilization, wastewater discharge and treatment and water environmental protection. It requires reducing freshwater and groundwater usage in all sectors of consumption. Developing sustainable water supply systems is a growing trend, because it serves people's long-term interests. There are several ways to reuse and recycle the water, in order to achieve long-term sustainability, such as:
  * Gray water re-use and treatment: gray water is wastewater coming from baths, showers, sinks and washbasins. If this water is treated it can be used as a source of water for uses other than drinking. Depending on the type of gray water and its level of treatment, it can be re-used for irrigation and toilet flushing. According to an investigation about the impacts of domestic grey water reuse on public health, carried out by the New South Wales Health Centre in Australia in the year 2000, grey water contains less nitrogen and fecal pathogenic organisms than sewage, and the organic content of grey water decomposes more rapidly.
  * Ecological treatment systems use little energy: there are many applications in gray water re-use, such as reed beds, soil treatment systems and plant filters. This process is ideal for gray water re-use, because of easier maintenance and higher removal rates of organic matter, ammonia, nitrogen and phosphorus.
  Other possible approaches to scoping models for water supply, applicable to any urban area, include the following:
  * Sustainable drainage system
  * Borehole extraction
  * Intercluster groundwater flow
  * Canal and river extraction
  * Aquifer storage
  * A more user-friendly indoor water use
  The Dublin Statement on Water and Sustainable Development is a good example of the new trend to overcome water supply problems. This statement, suggested by advanced economies, has come up with some principles that are of great significance to urban water supply. These are:
  # Fresh water is a finite and vulnerable resource, essential to sustain life, development and the environment.
  # Water development and management should be based on a participatory approach, involving users, planners and policy-makers at all levels.
  # Women play a central part in the provision, management and safeguarding of water. Institutional arrangements should reflect the role of women in water provision and protection.
  # Water has an economic value in all its competing uses and should be recognized as an economic good.
  From these statements, developed in 1992, several policies have been created to give importance to water and to move urban water system management towards sustainable development. The Water Framework Directive by the European Commission is a good example of what has been created there out of former policies.