Urbanization and Water

Urbanization is the process of a population shifting from rural to urban areas. The world is currently undergoing the largest shift of population placement and urban growth in history. More than half of the world's population now lives in towns and cities, and it predicted that by 2050 about 65% of the developing world and 86% of the developed world will be urbanized. The United Nations predicts that nearly all global population growth between 2015 and 2030 will reside in cities. Much of this urbanization will occur in previously undeveloped places such as Africa and Asia.

Urbanization ripples into a range of topics, including geography, sociology, economics, urban planning, and public health. It brings huge social, economic, and environmental changes. While urbanization has provided us with many opportunities for sustainable living and development, more often than not, we have fallen through on these opportunities and only created more problems.

Water quality has been largely affected by urban growth. Some water quality issues that relate to urban growth include:

Population Growth

The more people move into an area, the more an area must be developed and the more facilities must be built to support this population. These facilities include housing developments, roads, shopping areas, and commercial and industrial facilities, all of which require water to build and maintain. All of these facilities require plumbing and running water. Supplying more people with water puts stress on the water quality and supply. For example, Atlanta, Ga., one of the fastest growing metropolitan areas in the world, had to restrict development in the late 1980s because water-supply systems were not in place to handle the rapidly expanding growth in northern Atlanta. For much of 1997, the city was fined daily for releasing water with high levels of bacteria. When you have a booming population, it becomes difficult to keep up with the necessary facilities to keep water safe and uncontaminated. 

Erosion and Sedimentation
Development causes an increase in erosion because it removes the roots that hold soils in place.

Nitrogen

Nitrogen can be introduced through sewage and fertilizers. Heavy rains generate runoff containing these materials and allowing them to leach into nearby streams and lakes. Wastewater treatment facilities do not always remove excess nitrogen, which can lead to excess levels of nitrogen in surface or groundwater. Excess nutrients can cause eutrophication in aquatic ecosystems, which is a reduction in dissolved oxygen in water caused by an increase of organic nutrients. Nitrate can get into water as a result of runoff from fertilizers and also from the atmosphere. The atmosphere carries nitrogen-containing compounds derived from automobiles and other fossil-fuel burning sources. More than 3 million tons of nitrogen are deposited into the atmosphere each year by the United States, mainly derived from the combustion of fossil fuels. 

Phosphorous
Phosphorous can be found in agricultural fertilizers, manure, sewage and industrial wastes. Too much phosphorous in aquatic ecosystems can cause eutrophication. Soil erosion is a major contributor to this problem. Industries and automobiles that burn fossil fuels are a major player in the phosphorous cycle imbalance. 

Urban Runoff
Development causes increased erosion and sedimentation. When you pave a piece of land, that land becomes impermeable. This means that rainwater cannot reach the ground underneath the pavement, therefore it runs on top of the pavement until it reaches a soil it can absorb into. While the water runs along the pavement, it picks up pollutants along the way, including gasoline, plastics, and rubber. When the water finally reaches a soil or a river, it is carrying a whole slew of pollutants.

Sewage Overflows
There are three types of sewer systems:

1. Storm sewers carry storm runoff from streets, parking lots, and roofs through pipes and ditches, and eventually into streams.

1. Sanitary sewers carry raw sewage from homes and businesses to waste water-treatment facilities.

1. Combined sewers carry a combination of raw sewage and storm water runoff.

There are currently many adverse health affects to urbanization, but it doesn't have to look like this. With proper and sustainable planning, we can transform what the urban area looks like and what it means for the rest of our environment.

Blockages, inadequate carrying capacity, leaking pipes, and power outages at pumping stations often lead to sewage overflows into nearby stream. A rapid increase in population can leave these systems old, dirty, outdated, and more likely to cause problems. 

Waterborne Pathogens

Waterborne pathogens are disease-causing bacteria, viruses, and protozoans that are transmitted to people when they consume untreated or inadequately treated water. Cities routinely monitor the water supply to assure people are safe from waterborne pathogens, but with a rapid increase in a city's population, keeping up can be difficult. 

This picture shows a warning sign that has been put up alongside a stream near downtown Atlanta, Ga. Overflow of sewage has caused high bacteria levels in this stream. Urban runoff, sewage overflows, and waterborne pathogens are all very closely related when it comes to the quality of water in urban areas. 

Pesticides

Pesticides are heavily used in big agriculture, and we see a huge increase in the amount of pesticides used to grow our food since people stopped growing their own. In urban areas, the main use of pesticides is for residential and commercial uses (lawns, landscaping, etc). when a storm hits, these chemicals run off yards and into streams where they harm aquatic life and contaminate drinking water. 

Sources: 
The USGS Water Science School
UN Water
Global Water Partnership