Applied Sciences

5 Sustaining Our Freshwater Resources

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Learning Outcomes

After reading this chapter, you should be able to

• Describe how New York City worked with nature to improve its water supply. • Illustrate the water cycle and how the planet’s water is distributed. • Define different types of water use. • Analyze the methods used to meet global water demand. • Describe the potential for global conflict over water. • Describe different types of water pollution and ways to manage that pollution. • Differentiate between the hard path and soft path approaches to water management. • Discuss the role of forests in water management.

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Section 5.1 Case Study: New York City’s Water Supply

When viewed from space, Earth is a watery planet, with oceans covering over 70% of the planet’s surface and glaciers, ice caps, lakes, rivers, and streams covering another 10%. Yet water shortages and access to clean, safe drinking water are a serious problem in virtually every region of the world. The abundance of ocean water is too salty for human use, and much of the freshwater is either polluted or inaccessible.

Given its importance and critical role in all human life, it is remarkable how poorly managed water is as a resource. We regularly use rivers, streams, and the oceans as a dumping ground for our wastes and allow contaminants like spilled oil and agricultural chemicals to pollute critical groundwater supplies. We dam rivers and use massive amounts of energy to pump water hundreds of miles to irrigate golf courses and suburban lawns in the middle of deserts. And we pay little attention to how the management—or mismanagement—of natural capital resources like forests, wetlands, and other open spaces impacts water quality in surrounding regions.

This chapter will examine issues of freshwater management and consider the challenges of both water quantity and water quality. The next chapter will examine issues and challenges associated with our oceans.

We will first discuss issues of water quantity, which involve ensuring that there are adequate supplies and that mismanagement of water does not result in flooding. Only a tiny fraction of water on the planet is accessible and suitable for human consumption, making wise water management a critical priority. We’ll also see that just as with other critical resources like food and energy, water use varies greatly in different regions of the world. We will then con- sider issues of water quality, which involve ensuring that water is safe to use. Lastly, we will look at ideas and approaches for water conservation and sustainable water management, including efforts both to increase the availability of water on the supply side and to reduce usage on the demand side.

5.1 Case Study: New York City’s Water Supply

New York City has long prided itself on the quality of its municipal drinking water, with some residents and city boosters going so far as to call it the “champagne of tap water.” Over the years the city has garnered awards for the quality of its water relative to other major cities in the United States, and chefs and food experts have debated whether the city’s water might have something to do with the quality of its pizza and bagels. A Southern California–based pizza business even goes so far as to spend $10,000 a year to have New York City tap water trucked across the country to use in making dough for its New York–style pizza.

The story of why New York City’s water quality is so good and how the city addressed contam- ination can help us begin to understand the issues discussed in this chapter and the impor- tance of sustaining freshwater resources.

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Section 5.1 Case Study: New York City’s Water Supply

Building a Water Supply System As far back as the 1830s, city leaders in New York knew that, in order for the city to grow and thrive, they needed to do something about their water supply situation. At the time, the city drew its water from a patchwork of ponds, springs, and underground wells, but overuse and poor waste management were affecting both the quantity and the quality of the city’s water supply. Massive fires burned through wood-framed buildings because water pressure was too low to fill fire hoses. Overpumping of wells led freshwater levels to fall below sea level, allowing the nearby ocean to seep in and contaminate groundwater supplies. The raw sew- age and animal waste being dumped in the streets ran off and contaminated ponds and small reservoirs.

After a cholera epidemic (due in large part to poor water quality) killed thousands in 1832 and the Great Fire of New York burned 17 city blocks in 1835, city leaders embarked on a massive water development project that would change the course of New York City history. A dam was built on the Croton River north of the city, and a 65-kilometer (40-mile) covered aqueduct was built to carry water from there to the middle of Manhattan, where Central Park is located today. When the new water supply system opened in 1842, it carried 340 million liters (90 million gallons) of clean water every day to the thirsty city.

Sixty years later, the system was expanded on as city officials sought to prevent water shortages and inadequate supply while New York City grew and expanded. Water development projects were undertaken fur- ther north and west of the city in the Catskill Mountain region. An entire series of dams, reservoirs, aqueducts, and tunnels were constructed in the early 1900s, and by 1915 the Catskill Aqueduct was in operation.

Today New York City’s water supply system is still based almost entirely on the projects from the 1800s and early 1900s. Each day over 4.5 billion liters (1.2 billion gallons) of water are delivered to New York City’s 9 million residents, with 10% of this water coming from the Croton portion of the system and 90% originating from the Catskill portion. The Catskill watershed region, over 160 kilometers (100 miles) away from the city, draws water from 19 reservoirs and 3 lakes spread out over a 500,000-hectare (2,000-square-mile) area. A watershed is an area of land where sources of water (streams, creeks) flow together to a single destination. These lakes and reservoirs are connected to the city by 10,000 kilome- ters (over 6,200 miles) of pipes, tunnels, and aqueducts. Because of differences in elevation, almost the entire system moves water through gravity, with a drop of water taking anywhere from 3 months to 1 year to travel from an upstate lake or reservoir to a customer in the city. As the water approaches the city, it’s treated with chlorine to kill germs and pathogens, as well as fluoride for dental health and a couple of other chemicals to prevent corrosion of pipes.

Elizabeth Petrozello/iStock /Getty Images Plus The Ashokan Reservoir in the Catskill Mountains is one of several to provide New York City with its water supply.

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Section 5.1 Case Study: New York City’s Water Supply

Unlike most major urban water systems, New York City’s drinking water is not filtered. In fact, New York has the largest unfiltered drinking water system in the United States. New York’s water supply reservoirs were built in upstate areas that were covered in forests and that also had vast areas of intact wetlands. These forests and wetlands act as natural sponges and filters, absorbing rainfall and snowmelt and purifying the water in the process. Many other cities that draw their drinking water from nearby lakes and rivers need to have expensive fil- tration systems to remove sediment and other particles and contaminants before distributing water to residents.

Learn More: New York City’s Water Supply

To get a sense of how vast the Catskill watershed region is, visit the following link:

https://www.dec.ny.gov/docs/water_pdf/nycsystem.pdf

Expanding Ecosystem Management By the 1990s, however, things began to change for the worse in terms of New York City’s drinking water. Increased development, road building, suburban sprawl, and other activities in the Catskill region were having a negative impact on water quality in surrounding reser- voirs and lakes. U.S. Environmental Protection Agency (EPA) inspectors warned the city that it might have to build a $10 billion water filtration plant to address the issue.

Instead, New York City decided to take a different approach. The 1997 Watershed Memoran- dum of Agreement (MOA) was negotiated between New York City, New York State, the EPA, environmental groups, and municipalities and townships in the Catskills region. The MOA committed New York City to spend just under $2 billion on a range of initiatives intended to improve water quality in the Catskill reservoirs. These initiatives included purchasing and protecting lands surrounding reservoirs and lakes, as well as paying nearby landowners who agreed not to develop their lands commercially. In addition, the city helped upstate communi- ties improve wastewater treatment plants, assisted dairy farmers with manure management, and worked with road departments to ensure that runoff from roads and highways was not entering reservoirs. Lastly, the city provided funding for upstate home owners to upgrade sep- tic systems and for forest landowners to improve forest management practices. Collectively, these approaches are known as ecosystem management because they focus on maintaining water quality at the source rather than cleaning the water as it reaches its destination. Over the past 20 years, the ecosystem management initiatives undertaken as part of the MOA have proved effective enough that the EPA has granted New York City a series of “filtration avoid- ance determinations” that allow the city to operate its water system without a filtration plant.

The ecosystem management approach has been supplemented with high-tech features, including a network of hundreds of robotic buoys deployed across reservoirs to continually test and monitor water quality. These robotic water quality monitors test over 1.9 million water samples each year. In addition, the city has recently put in place the world’s largest ultraviolet water disinfection facility. Water passes through containers mounted with ultra- violet lights that kill any microorganisms that might contaminate the water and make con- sumers sick.

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Section 5.2 Freshwater Systems

While New York City water officials must always be vigilant in ensuring the quality of the city’s water, the success of the MOA initiatives points to the importance of “source manage- ment” as an approach to meeting our water needs. Rather than spend $10 billion building a water filtration plant to treat polluted water at the back end of the system, New York City spent one fifth of that amount to ensure that its drinking water was not polluted at the source in the first place. Essentially, New York City has been investing in the natural capital resources of forests and wetlands in the Catskills region and letting this natural infrastructure provide the ecosystem service of keeping the city’s water clean.

5.2 Freshwater Systems

Water is perhaps the most critical resource to human well-being and survival. Our bodies are made up of as much as 60% water, and while healthy individuals can survive weeks without food, they would last only a few days without water. We also rely on water to grow food, produce energy, and manufacture just about everything imaginable. In addition, we depend on and benefit from a range of ecosystem functions and services provided by water, includ- ing transportation, recreational activities, and wildlife habitat. We regularly rely on rivers, streams, and oceans to dilute and purify our waste products, although this use frequently conflicts with the other ecosystem functions and services that water provides. Despite all the ways we depend on water, we seldom give much thought to where it comes from and how it gets to us.

Water Distribution It’s been said that we live on a “blue planet,” since water covers nearly three fourths of the Earth’s surface. However, when we account for where water is located and what condition it is in, we realize that water is not only a critical natural capital resource but also a scarce one. How can it be that such an abundant resource can also be scarce at the same time?

Imagine the world’s water as 1 million individual 1-gallon containers. (In reality, there are 370 million trillion gallons.) For starters, about 970,000 (97%) of those containers would be filled with salty ocean water unsuitable for human consumption. It was this reality that inspired the line from The Rime of the Ancient Mariner, “water water everywhere, nor any drop to drink” (Coleridge, 1919/1990, lines 121–122). Another 26,100 gallons (2.61%) would be filled with ice and snow—nearly all of it from ice caps and glaciers in the Arctic and Antarctic regions, far from major human populations. Roughly 3,600 gallons (0.36%) would be filled with groundwater, with much of this (but not all, as we will learn) consisting of salt water also unsuitable for human consumption.

Out of the 1 million gallons we started with, only 300 gallons remain. Some of those 300 gal- lons consist of water vapor in the atmosphere, water found in saline or salty lakes, or water in the soil, leaving just about 180 gallons (0.018%) of fresh surface water—water on the surface of the Earth, found in rivers, wetlands, lakes, and reservoirs. Because this fresh sur- face water is the primary source of water for most people on the planet, we can see just how scarce and precious this resource actually is. (See Figure 5.1.)

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Section 5.2 Freshwater Systems

Thankfully, nature has a way of constantly recycling, replenishing, and purifying water sources. In fact, unlike other resources (such as fossil fuels) that are permanently “consumed,” global water supply is more or less fixed. This is because of the global hydrologic cycle. The hydro- logic cycle, or water cycle, describes the movement of water between the planet’s surface, atmosphere, soil, oceans, and living organisms. If we think again of our 1 million gallon con- tainers, the water cycle is constantly moving water among the different containers, although human activities are increasingly interfering with this process and further complicating effec- tive water management.

Water Cycle The global water cycle is driven primarily by solar energy. Heat from the sun causes water to evaporate from surface waters and land surfaces and enter the atmosphere as water vapor. For example, it’s estimated that solar energy evaporates roughly 425,000 cubic kilometers (km3) of ocean water each year. To put that in perspective, just 1 cubic kilometer of water is

Figure 5.1: Water distribution

Only 0.6% of the world’s freshwater—0.018% of all water on Earth—is readily available as surface water for human use.

Source: Data adapted from “Where Is Earth’s Water?” by US Geological Survey, n.d. (https://www.usgs.gov/media/images/distribution -water-and-above-earth).

Earth’s water

Freshwater 3%

Other 0.4%

Fresh surface water (liquid)

0.6%

Ice caps and glaciers

87%

Groundwater 12%

Saline (oceans)

97%

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Section 5.2 Freshwater Systems

equivalent to a tank of water that is 1,000 meters (3,280 feet) tall, wide, and long, or 1 tril- lion liters (265 billion gallons). The amount of energy it takes to move this much water from the ocean to the atmosphere is massive. Roughly one third of all the solar energy striking the Earth each day is used to drive evaporation.

In addition to evaporation, plants draw massive amounts of water from the soil and release some of that water to the atmosphere as water vapor through a process known as transpira- tion. Evaporation and transpiration are together known as evapotranspiration. As water vapor from evapotranspiration rises into the atmosphere, it cools and condenses to form clouds (condensation) before falling back to Earth as rain and snow (precipitation). Evapo- ration, transpiration, condensation, and precipitation form the basis of the water cycle (see Figure 5.2).

Figure 5.2: The water cycle

The basis of the hydrologic cycle is condensation, precipitation, and evapotranspiration. Once water reaches the ground, it either runs off into nearby bodies of water or infiltrates the surface, where it reaches the water table and underground aquifers.

Source: Based on “Ground Water and Surface Water a Single Resource,” by US Geological Survey, 2013 (https://pubs.usgs.gov/circ /circ1139/).

Groundwater flow

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The processes of evaporation and condensation purify water naturally because only water molecules are pulled into the atmosphere, leaving any salts, contaminants, or pollutants behind. This is basically the same as making distilled water by boiling water and condensing the vapor. Roughly 90% of the ocean water evaporated each year falls back as precipitation over the oceans, where it mixes again with salt water. However, about 10% of that moisture falls over land surfaces as freshwater precipitation.

An even larger amount of freshwater precipitation is provided by evapotranspiration from plants and forests. In tropical forests as much as 80% of all precipitation comes from the direct recycling of evapotranspiration from plants. This feedback loop—more trees leading to more transpiration leading to more precipitation leading to more trees—is a key reason why forest management is so tightly linked with water management.

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Section 5.2 Freshwater Systems

Overall, of the 110,000 km3 of precipitation that falls over land surfaces each year, it’s esti- mated that roughly one third comes from moisture drawn from ocean waters and two thirds from moisture from evapotranspiration from plants. This 110,000 km3 of precipitation ends up doing one of three things. First, about two thirds of that water evaporates back into the atmosphere from land surfaces or through plant transpiration. The other one third either flows over land and enters rivers, streams, and lakes (surface water) or gradually percolates through soil and rock to enter underground aquifers (groundwater). It’s this relatively small amount of water, roughly 37,500 km3 per year, that replenishes the tiny sliver of fresh surface water illustrated in Figure 5.1 and represents the total renewable supply of fresh surface water on the planet. As with most other resources, this freshwater supply is unevenly dis- tributed around the world. Atmospheric circulation patterns, topography, and proximity to water sources and forests are all factors that influence the amount of precipitation in a given location.

Human Impact on the Water Cycle Human activities can also affect precipitation patterns and what happens to that precipitation after it falls to Earth. Under normal conditions, as precipitation reaches the ground, some of it is pulled below the surface by gravity through a process known as infiltration. This water eventually reaches the water table, a depth below ground where soil and rock are completely saturated with water. The saturated area immediately below the water table is known as an aquifer, an area of permeable rock and sediment from which water can be extracted.

Many communities, private home owners, factories, and farmers use pumps to pull ground- water from aquifers to the surface. As long as rates of infiltration are the same or greater than rates of extraction, the water level in the aquifer will be maintained. However, this is often not the case, and overpumping is resulting in aquifer depletion in many locations, such as with the Ogallala Aquifer in the U.S. Midwest (recall Chapter 4). As New York City discovered in the 1830s, overpumping of water from aquifers near the ocean can also cause the problem of saltwater intrusion as lower freshwater levels in the aquifer allow adjacent salt water to enter and contaminate that supply. Saltwater intrusion is a worsening problem in coastal regions around the world today.

Land use on the surface also affects how quickly aquifers can recharge. Developed areas like cities and suburbs have replaced grassland and forest soils with a lot of imper- meable surface area. Most roads, driveways, parking lots, and roofs of buildings do not allow rain and melting snow to infiltrate into the ground and instead increase run- off. This increased runoff can result in more floods as too much water moves too fast across the surface and is not absorbed into the ground. Recent research demonstrates how too much impermeable surface area greatly worsened the impacts of Hurricane Harvey in Houston in 2017 (Zhang, Villarini,

Cameron Whitman/iStock/Thinkstock Heavily developed and paved areas create a problem for our water supply, since rain and snow cannot easily penetrate back into the Earth.

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Section 5.3 Global Water Use and Demand

Vecchi, & Smith, 2018). More and more cities, municipalities, developers, and home owners are beginning to consider ways to cut down on water runoff and increase rates of infiltration in order to increase and improve groundwater supplies as well as prevent flooding.

The water cycle makes available the freshwater that all human life relies on, constantly recy- cling and replenishing this scarce resource. Unfortunately, human activities such as over- pumping of groundwater and paving of surface areas are negatively impacting both the quan- tity and quality of our water supply. This is happening at the same time that global water use and demand is increasing with population growth. The next section takes a closer look at global water use and how that demand can be met, given the finite supply of freshwater available to us.

5.3 Global Water Use and Demand

Recall that an estimated 110,000 km3 of precipitation falls over land surfaces each year and that 37,500 km3 of this enters surface waters or percolates into underground aquifers. This 37,500 km3 represents the theoretical supply of renewable freshwater on the planet each year. If all this water were available to us, it would be more than enough to meet human needs. However, a few factors complicate this picture.

First, where this precipitation falls does not always align with where humans reside. For example, large amounts of precipita- tion fall to the ground and flow to the sea in sparsely populated regions of the Ama- zon basin in South America or in remote areas of central Africa. Second, when this precipitation falls can make water manage- ment challenging even in very wet places. For example, in tropical regions of Asia that experience heavy rainfall, as much as 80% to 90% of annual precipitation can fall dur- ing just a few months of the monsoon, with relatively dry conditions prevailing for the other months of the year.

As a result, and despite adequate supplies of water on average globally, we face water short- ages and scarcity in many regions. Over 2 billion people lack access to adequate and safe water supplies, and over 4 billion lack access to proper sanitation (World Water Assessment Pro- gramme, 2019). As a result, at least 2 million preventable deaths occur each year from water- related diseases that mostly claim the lives of young children (WHO, n.d.b). In some cases, problems arise from an absolute scarcity of water, whereas in others there is inadequate infra- structure to meet a population’s water requirements. This section will consider those issues of water quantity: its use and demand and how human water needs are being met.

Antoninapotapenko/iStock /Getty Images Plus Tropical regions such as Asia can get 80% to 90% of their total annual rainfall in as little as 3 months due to natural weather conditions.

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Section 5.3 Global Water Use and Demand

Let us return to the 37,500 km3 that represents the theoretical supply of renewable fresh- water each year. As much as half runs off the surface and to the sea in uncaptured floodwa- ter. Humans build dams and other barriers to try to capture some of that runoff, but as we will discuss, that brings its own problems and challenges. Another 20% of the 37,500 km3 of global freshwater supply is in regions that are not readily accessible. That leaves us with roughly 12,500 km3 of what is known as reliable surface runoff, and it is this amount that is actually available for human use and consumption. So how do we make use of this reliable surface runoff? What are the environmental impacts of that use? And why do so many people around the world still face water scarcity and shortages?

How Water Is Used Because we use and rely on water in so many different ways, we can measure water consump- tion differently as well. For starters, it’s estimated that humans already appropriate over half of the 12,500 km3 of reliable surface runoff each year, leaving less than half for all other spe- cies and organisms on the planet. We can first divide that human use or appropriation into two broad categories: instream uses and extractive uses.

Instream uses of water refers to the ways in which we use water without actually extracting it from its physical location. For example, water-based recreational activities like boating and waterskiing are common on many lakes and rivers in countries like the United States. While these activities do not involve a direct consumption of water, they may compete with or pre- vent the use of that water for other purposes.

Extractive uses of water refers to situations in which water is physically removed from its source location. In some cases this involves actual consumption, while others involve using and then returning the water to its source. For example, when water is extracted from a river or aquifer and used to irrigate a farm field, most of that water will evaporate to the atmo- sphere. This represents a consumptive use of water. In contrast, hydroelectric power plants divert large amounts of water from rivers and lakes to generate electricity (see Section 7.12), but that water flows back to the same river or lake. This represents a nonconsumptive use of water. The Apply Your Knowledge feature examines the environmental impact of noncon- sumptive use.

Apply Your Knowledge: What Is the Environmental Impact of Nonconsumptive Water Use?

You can probably imagine the environmental impacts of chemical pollution and water consumption, but what about nonconsumptive water use?

To explore this question, consider the Brazilian Nuclear Power Plant (BNPP) in southeastern Brazil. The facility withdraws water from Ilha Grande Bay to cool equipment. Afterward, that water is returned to the bay. Aside from a small amount of water that is lost to evaporation, no materials are added or removed during the process.

(continued)

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Section 5.3 Global Water Use and Demand

Apply Your Knowledge: What Is the Environmental Impact of Nonconsumptive Water Use? (continued)

In a 2012 study, researchers investigated the environmental impacts of BNPP on Ilha Grande Bay (Teixeira, Neves, & Araújo, 2012). Researchers collected measurements of fish biodiversity and abundance near the power plant (within 200 meters) and in similar environments farther away (more than 1,500 meters). They then compared the two locations to highlight any differences. Some of these results are shown in Figure 5.3.

Figure 5.3: Impact of BNPP on biodiversity and fish abundance

Species biodiversity (a) and fish abundance (b) in Ilha Grande Bay. “Close” locations are less than 200 meters and “far” locations more than 1,500 meters from the BNPP facility.

Source: Data from “Thermal Impact of a Nuclear Power Plant in a Coastal Area in Southeastern Brazil: Effects of Heating and Physical Structure on Benthic Cover and Fish Communities,” by T. P. Teixeira, L. M. Neves, and F. G. Araujo, 2012, Hydrobiologia, 684.

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Section 5.3 Global Water Use and Demand

Apply Your Knowledge: What Is the Environmental Impact of Nonconsumptive Water Use? (continued)

The first chart suggests that there is significantly less biodiversity (fewer species of fish) close to the power plant than there is farther away. In the second chart, the difference between the two measurements is small compared with the uncertainties of the two measurements. There appears to be a similar number of fish in both locations.

Take a moment to consider this data along with what you know about water use in this location. Can you explain how the power plant might be impacting fish in the surrounding ecosystem?

The power plant is affecting ecosystems by altering environmental conditions. According to the temperature data in the Ilha Grande Bay study, the water near BNPP is more than 4 degrees Celsius warmer than its surroundings (see Figure 5.4).

When the power plant cools off its equipment, the process warms the water that is extracted. This raises the temperature of bay locations with close proximity to BNPP. While many fish species can survive the cooler temperatures of the greater bay, relatively few have been able to thrive close to the power plant. With less competition, the species that can tolerate the warmer water are also able to achieve larger populations than they do elsewhere. The result is an environment that still has life but that is severely diminished in terms of biodiversity.

Figure 5.4: Impact of BNPP on water temperature

Temperatures at Ilha Grande Bay study locations.

Source: Data from “Thermal Impact of a Nuclear Power Plant in a Coastal Area in Southeastern Brazil: Effects of Heating and Physical Structure on Benthic Cover and Fish Communities,” by T. P. Teixeira, L. M. Neves, and F. G. Araujo, 2012, Hydrobiologia, 684.

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