In most cases the water quality is unfit for human consumption. The principal cause of water scarcity is the growth in demand. Water is taken from remote areas to satisfy the needs of urban areas. Another reason for water scarcity is climate change: precipitation patterns have changed; rivers have decreased their flow; lakes are drying up; and aquifers are being emptied. Governmental issues In developing countries many governments are corrupt and poor and they respond to these problems with frequently changing policies and non clear agreements. Water demand exceeds supply, and household and industrial water supplies are prioritised over other uses, which leads to water stress. Potable water has a price in the market; water often becomes a business for private companies, which earn a profit by putting a higher price on water, which imposes a barrier for lower-income people. The Millennium Development Goals propose the changes required. Goal 6 of the United Nations' Sustainable Development Goals is to "Ensure availability and sustainable management of water and sanitation for all". This is in recognition of the human right to water and sanitation, which was formally acknowledged at the United Nations General Assembly in 2010, that "clean drinking water and sanitation are essential to the recognition of all human rights". Sustainable water supply includes ensuring availability, accessibility, affordability and quality of water for all individuals. In advanced economies, the problems are about optimising existing supply networks. These economies have usually had continuing evolution, which allowed them to construct infrastructure to supply water to people. The European Union has developed a set of rules and policies to overcome expected future problems. There are many international documents with interesting, but not very specific, ideas and therefore they are not put into practice. Recommendations have been made by the United Nations, such as the Dublin Statement on Water and Sustainable Development. Optimizing the water supply network The yield of a system can be measured by either its value or its net benefit. For a water supply system, the true value or the net benefit is a reliable water supply service having adequate quantity and good quality of the product. For example, if the existing water supply of a city needs to be extended to supply a new municipality, the impact of the new branch of the system must be designed to supply the new needs, while maintaining supply to the old system. Single-objective optimization