Designing and maintaining the urban water provision infrastructure is daily work for thousands of people in the US, including associations such as American Water Works Association (AWWA). Providing people with adequate freshwater becomes a challenge with the urbanization of the world. To meet this worldwide challenge, three conditions must be observed:
- Water availability : there must be an adequate volume of water available
- Quality : it must be clean enough to use, either before or after the treatment
- Delivery : the infrastructure must exist to deliver it where it is needed
The demographic reality of rapid urbanization
Rural-to-urban migration and the growth over time of families already in cities lead to an increasing and rapid urbanization. According to United Nations Development Programme (UNDP) 2009, between now and 2050, 3 billion more people will live in cities. This urbanization coupled with climate change, which makes dry periods of the year even dryer, will have consequences on urban water delivery systems.
There are three criteria that must be met to adequately provide residents with fresh water:
- Water availability
In 20 years, humanity has to build an urban water delivery system five times bigger, in terms of people served, than the one that has developed in Europe over the centuries.
Water shortages will become a burning issue in the world. They will result from two different occurences:
- Perennial water shortages: a recent study emphasized that there are 150 million people in cities with perennial water shortages, which means that there is not 100L/person/day available if all water within a greater metropolitan area is harvested. This number is going to rise to 993 million people in consequence of demographic growth and climate change.
- Seasonal water shortages: they are shortages lasting one or more months. They affect 886 million people in the developing world.
These calculations rely on the fact that cities can use all available water, essentially drinking rivers and streams dry. Overuse of these water sources would have consequences with the extinction of many freshwater species and the destruction of the natural benefits of freshwater systems (fishing, recreation). We must leave some baseline amount of water in a river system as an environmental flow to avoid damaging the ecosystem.
The amount of available water on the Earth’s surface compared with the location of major cities in the developing world. Yellow and orange indicate dry areas, green indicates moderate areas, and blue indicates major river systems. Urban areas are shown as red circles, with the diameter of the circles proportional to the population of the urban area.
A study in the journal Ambio (Mc Donald, 2011b) highlighted the fact that water quality problems are a growing issue in even more cities. Because of the urbanization, there is an increasing rate of density (people/hectare) upstream that leads to excessive nitrate concentrations, which is a detriment to drinking water.
Cities have relatively few resources to address water quality and water delivery issues. For example, water delivery challenges must be solved in Africa with roughly 1/200 of the economic resources as would be available in some developed countries.
To combine urbanization and water shortages, cities can use two different means:
- ‘’Gray’’ infrastructure solution: try to find new sources of water while mitigating the environmental impact of further water withdrawal and storage
- ‘’Green’’ infrastructure solution: try to change the way cities use water by using it more wisely. For example : improve the efficiency of agricultural irrigation
The challenge now is to face the coming global urbanization and climate change by finding a sustainable way to provide the cities with freshwater. Professional organizations such as AWWA or US Water professionals can act effectively in that way to find an adequate solution.
Information in this article is taken from October 2011, article ‘’The coming global urbanization: what it means for freshwater provision’’ by Robert McDonald, in Journal AWWA.