Half of humanity now lives in cities, and within two decades, nearly 60 per cent of the world's people will be urban dwellers. Urban growth is most rapid in the developing world, where cities gain an average of 5 million residents every month

The lack of adequate water and sanitation facilities leads to health issues such as diarrhoea, malaria and cholera outbreaks. Though water supply and sanitation coverage increased between 1990 and 2008, the growth of the world's urban populations jeopardizes those results. While between 1990 and 2008 1052 million urban dwellers gained access to improved drinking water and 813 million to improved sanitation, the urban population in that period grew by 1089 million people.

Those who suffer the most of these water-related challenges are the urban poor, often living in slum areas or informal settlements following rapid urban growth, in situations lacking many of life's basic necessities: safe drinking water, adequate sanitation services and access to health services, durable housing and secure tenure.

Urban water supply has a propensity to be affected by pressures on both the supply and the demand sides, which exposes vulnerabilities. On the supply side, effects are anticipated regarding the quantity, timing, and quality of source water. On the demand side, effects are expected in use patterns in response to climate impacts. For example, alterations of temperature and relative humidity, growing season duration, and precipitation patterns may lead to changes in water demand for municipal landscape irrigation.

Most studies of urban water supply system vulnerabilities to climate change are top–down as they have used scenarios from GCMs. In such a top–down approach, the climate change estimates of precipitation, temperature, and other meteorological parameters are used to drive a hydrologic model, which is then used to quantify changes in streamflow and reservoir water surface levels.

Heavy demand of water due to rapid increase of population and number of residents in the urban areas, shortage of water occurs. One of the best ways to face this situation is to recycle the used water.

Major Water Reforms in many Australian Cities are as follows:

Community engagement has played a significant role in urban water policy, particularly through the strong reliance on water restrictions as a means of ensuring the sustainable yield of urban water supply systems. This has required strong community involvement in reducing water use in periods of drought. It has also meant that there is strong public support for restrictions, even during periods of severe drought when there have been quite onerous requirements over a long period of time on householders, especially in terms of outdoor water use. Of course, these restrictions will impact differently in different areas depending on climate, soil type and outdoor landscaping preferences.

Innovative and robust methods of community engagement can and should be employed to determine community preferences regarding large-scale expenditure, environmental flows, reliability levels and levels of restriction. These methods should incorporate the three ideals of community engagement:

• Representativeness—a process involving the random selection of participants, and inviting those citizens who would not normally engage in these processes to have an opportunity to express their preferences in an informed way.
• Deliberation—a process in which engaged citizens have an opportunity to obtain information and increase their level of knowledge on issues by questioning stakeholders and experts, and by discussing and deliberating on the issues.
• Influence—involves the principle that the results of the engagement process be taken seriously by decision makers and are meaningful.

Because of a growing concern with the quality of some urban water supplies and reports that not all waters are as pure and safe as people have always assumed, the federal government passed the Safe Drinking Water Act in 1974. This law authorizes EPA to set minimum national drinking water standards.

The construction of dams, although initially motivated for power generation, creates reservoirs with multipurpose uses and functions, which include the availability of water to urban water supply and agriculture, the mitigation of devastating floods, navigation, and the support of leisure activities. The new habitats these water bodies create and their scenic value attract activities that produce waste.

All dams and reservoirs become a part of the environment, which they influence and transform to a degree and within a range that varies from project to project. Frequently seeming to be in opposition, dams and their environment interrelate with a degree of complexity that makes the task of the dam engineer particularly difficult.

Reservoirs can become the receiving body for urban, agricultural, and industrial wastewater. These wastes and the evolution of the water quality in the reservoir, due to the fact that the prevailing processes and characteristics change when water is stored and not flowing, cause changes in the quality of water discharged downstream.

 It is high time that we be mindful of our actions for we haven't inherited the Earth from our ancestors but borrowed it from our children.