Lesson 3.03 Sources of Drinking Water

Freshwater

Freshwater is often defined as water that has a very low salt concentration — usually less than 1%.

Humans and most other organisms cannot drink water from marine sources — saltwater — and survive. The high salt content in marine water draws the water out of cells when consumed causing the cell to wither and die. For this reason, most organisms need to consume water that has very little salt dissolved in it.

The main sources of freshwater that humans use for drinking are from groundwater and non-marine surface water in river, lakes, ponds, and streams. Remember from the previous lesson that most of the freshwater on earth that is available for human consumption is groundwater. However, the majority of the freshwater that we use and drink in our homes comes from rivers, lakes, and reservoirs dammed rivers because groundwater can be hard to access. In order to access groundwater, a well, shaft or hole, has to be dug far enough down in the ground to tap into the aquifer where the groundwater is stored. Also, not all areas have groundwater available or not enough of it to support use. However, some people, especially those in more rural areas, get their drinking water from groundwater. It is estimated that between 25-40% of the earth's drinking water comes from groundwater.

There are drawbacks to using both sources—groundwater and surface water—for drinking water. Both are susceptible easily affected, influenced, or harmed by something to shortages and pollution.

Water is a valuable, yet limited resource.

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Groundwater

Think back to the water cycle. Groundwater enters into the ground through the process of infiltration. This process takes time because the water has to filter through the soil and rocks in the ground to reach the aquifer where it is stored. As groundwater is used, it has to be replenished. If the groundwater is not replenished quickly enough, the well will stop producing water. This means that groundwater sources are susceptible to droughts. If precipitation is not occurring in an area, the groundwater is not being replenished.

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The depletion of groundwater can cause other environmental problems besides water shortages. When water is removed from the ground, sinkholes can occur. These sinkholes occur because the water that was applying an upward force on the ground above is removed causing the ground to become unstable which causes the ground to "cave-in" and form a hole. This can cause problems to cities' infrastructures—such as roads and utilities—and can cause damage to the habitats of organisms in the ecosystem.

Visit the Groundwater Foundation to learn interesting facts about groundwater.

Another threat to groundwater is contamination. Groundwater can be contaminated when man-made products get into the groundwater. Some examples of man-made products that contaminate groundwater are gasoline, synthetic chemical process by human means fertilizers, synthetic pesticides, road salt, and used motor oil. All of these substances can work their way into the groundwater over time, especially if they are not used properly and disposed of properly. Groundwater supplies can also be contaminated by untreated wastes from septic tanks that are not properly maintained or installed and from toxic chemicals in underground storage tanks, as well as, other chemical pollutants from "leaky" landfills. When these chemicals and substances enter the groundwater, they can cause serious health problems to humans and other wildlife that consume it. Visit Alabama Aquifers to see aquifer recharge areas areas that provide the water needed to resupply the aquifer for Alabama. Look at the map to see what the name of the aquifer recharge area is where you live.

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Surface Water

Much like groundwater, surface water depends on precipitation for its supply to be maintained. Therefore, just like groundwater, it is susceptible to drought. In drought situations, areas do not have a supply to replace the water that they are using. When this happens, there can be a shortage of water.

Rivers, lakes, ponds, and streams are supplied water through the runoff of precipitation and in some cases from groundwater in the form of natural springs. When it rains, the rain that does not soak into the ground is washed into nearby streams, lakes, ponds, and rivers. Areas that collect this runoff water are known as watersheds. Watersheds are sloped so that the water that does not soak into the ground filters into the nearby rivers, streams, lakes, and ponds.

When this water runs across the ground, it can become polluted. As the water moves toward the watershed, it picks up any chemicals, trash, salt, animal waste, and dirt (known as sediment) that are on the ground. These substances are then deposited into the water source polluting the water. Synthetic fertilizers can enter rivers and lakes in this manner and cause problems to the aquatic ecosystems. This fertilizer can cause an over growth of algal blooms. After the algae dies and settles to the bottom, the decomposers (bacteria) use up most of the dissolved oxygen in the water. This results in less oxygen for the fish that need it. This is referred to as eutrophication. This harms fish and other organisms that are in the water. If the water is consumed without being treated, these chemicals and substances can cause harm to humans.

Pristine clean and fresh, as if new pond and polluted pond showing signs of eutrophication

There are two basic types of pollution sources for surface water—point source pollution and non-point source pollution. Non-point source pollution is where there is not identifiable source and the pollution comes from a wide area and sources (runoff with chemicals, trash, and sediment). Visit EPA: What is Nonpoint Source Pollution to learn more about non-point sources and what can be done to prevent them.

Point source pollution has a single, identifiable source such as a pipe or drain discharging polluted material into the water. Water pollution is not just from chemicals, it can also be polluted by increasing its temperature. This can happen when the water that is used as a coolant for plants and factories is dumped into the water, increasing the water temperature.

Visit Watershed to learn about the Chesapeake Bay Watershed.

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