1. Bell Ringer
List at least TWO examples of density dependent limiting factors.
Using the graph to the right, predict what will happen to Hungary’s population.

2. Why is water so important to us, and how can we preserve it?
Human Usage of Water
Why is water so important to us, and how can we preserve it?

3. Water Resources
Recall our earlier studies of the water cycle. We examined the water cycle as a means of recycling fresh water on Earth.
In the water cycle, water evaporates from the planet’s bodies of water (mainly the oceans). Water then condenses and forms clouds; eventually, it falls back to Earth in the form of precipitation.
This runoff either forms surface or groundwater sources, or it returns to the oceans.

4. Water Resources

5. Water Resources
While fresh water is a renewable resource, it is still quite limited. 70% of the Earth’s surface is covered by water, but only 3% of all water is freshwater.
Furthermore, only 30% of all freshwater is accessible – most of it is frozen in glaciers and icecaps. Most of our accessible freshwater consists of groundwater.

6. Surface Water
Surface water sources include lakes, rivers, streams and wetlands.
Historically, cities were placed in close proximity to water sources, especially rivers. Even today, most large cities depend on surface water for operation.
Water is used not just for drinking, but for agricultural and industrial processes, as well as a source of food and transportation. We will discuss this in greater detail later.

7. Surface Water
Rivers and streams form from runoff, melting snow, and groundwater. Streams eventually combine to form tributaries and rivers.
A network of flowing water is called a river system. Each river system drains the land around it; the area of land being drained is called a watershed.

8. Surface Water

9. Groundwater
Most of our available fresh water is located underground. Groundwater is formed when water percolates through the soil, and collects within sedimentary and rock formations.
As water collects in groundwater sources, it begins to saturate the rock and soil around it. The water table is the boundary between fully saturated and unsaturated earth.

10. Groundwater
Despite its name, the water table is not level, and it is not static. It changes due to geography, rainfall conditions and human interaction.
When the water table reaches the surface, springs, rivers, lakes and oases can form.

11. Groundwater
A fully underground formation of groundwater is called an aquifer. Aquifers are often found in rock, sand and gravel, since these materials often have space where groundwater can accumulate.

12. Groundwater
Many different types of rocks have small pores, where water can leak through. Porosity is the percentage of a rock’s volume that is made up of pores and empty space.
The greater a rock’s porosity, the more water it can hold before it becomes saturated.

13. Groundwater
Permeability is the ability of rock or soil to allow water to pass through them.
For instance, gravel is permeable, since it permits water flow. In contrast, clay and granite are not.
As a result, aquifers tend to form within permeable materials, and can be contained around impermeable materials.

14. Groundwater
The land right above an aquifer (where water trickles down into the aquifer) is called the recharge zone.
Recharge zones are particularly vulnerable, since pollution typically enters the aquifer at this point.

15. Groundwater
Human development can also block up the recharge zone. This is common with parking lots, which contain impermeable materials.
Note that aquifers often take a long time to recharge. As such, it is vital to protect recharge zones to the best of our ability.

16. Water Use and Management

17. Human Water Usage
People have three major uses for water: residential, agricultural and industrial.
Although most fresh water worldwide is used for irrigation, local water usage does fluctuate with availability of water, local population size, and economic conditions.
For instance, compare Asia and Europe’s water use; Asia uses over 80% of its fresh water for agriculture, while Europe only uses 34% of its fresh water for this purpose.

18. Residential Water Usage
Residential water use includes all personal use of water, both inside (drinking, cooking, cleaning) and outside (grounds keeping, maintenance) the home.
Residential water use is a small proportion of total water use all other the world. Latin America and Oceania use the highest percentage of water for residential use (~20%), while Asia and Africa use the lowest percentage (~10%).

19. Residential Water Usage
Most water for residential use that has been treated to the point it can be safely drank is considered potable.
Water treatment removes pathogens – organisms that can cause disease – as well as hazardous materials, like mercury, arsenic and lead.
We will discuss water treatment in greater detail when we look at water pollution.

20. Industrial Water Usage
Worldwide, 19% of all fresh water is used for industrial processes. Industrial water use contains three major factors:
Manufacturing of goods
Waste disposal
Generation of power/electricity

21. Industrial Water Usage
Most industrial water is used to cool power plants. Water is often pumped from a river or lake, and is pumped back after it runs through a cooling tower.
While this water is typically clean and reusable, it can also be a major source of thermal pollution.

22. Agricultural Water Usage
Two-thirds of all fresh water around the world is used for agriculture. Irrigation is the process of providing water to plants (outside of typical rainfall).
However, many irrigation systems are not efficient. In a poor system, as much as 80% of the irrigation water evaporates, never reaching a root system.
High-pressure sprinklers are a common example of poor irrigation.
Many irrigation techniques are used today, often depending on crops and geography.

23. Water Management
Water management projects are meant to meet the needs of human water supply.
This can include anything from providing potable water for consumption, to providing irrigation water for crops in an arid region, to providing hydroelectric energy.
Water management projects are vital for allowing human communities to exist in regions relatively far from obvious water sources.

24. Water Management
Water diversion refers to channeling all or part of a river into man-made canals. This is done to tap the water for consumption, irrigation or energy production.
Excessive diversion can result in drying up the river, and as a result, drying up wetlands and floodplains that depend on the river’s water flow to exist.
For example, the Colorado river has been so heavily diverted that the river no longer reaches the Gulf of California, except in the wettest months.

25. Water Management
This is a photograph of a diversion dam along the Colorado River. Note how it draws water away from the river’s natural water flow.

26. Water Management
Dams, as discussed previously, are used to limit a river’s natural flow. Once a river is dammed up, a reservoir (artificial lake) is formed behind the dam.
Reservoirs can provide water for residential, industrial and agricultural use. By hindering the river’s flow, they also provide a means of flood control.
However, they also disrupt communities and ecosystems behind and in front of the dam.

27. Water Management
Water conservation is the act of rationing water sources, either by:
Limiting water use
Increasing the efficiency of agricultural, residential or industrial processes
Reusing or recycling water sources

28. Water Management
While households use the least amount of fresh water overall, it is easiest for humans to reduce water use through household water conservation.
Water-efficient technology helps to reduce the water used in common processes. Good examples are efficient toilets, shower heads or washing machines.

29. Water Management
As one-third of a typical household’s water use is spent on landscaping, xeriscaping – the act of designing a landscape with minimal water use – can significantly reduce water intake.
When watering landscapes or plants, it is best to do so in the early morning or evening, to prevent water loss due to evaporation.

30. Water Management
As water intake continues to increase, people are beginning to tap new resources.
Desalination is the act of removing salt and heavy minerals from “hard” (mineral) water. Hard water is often brackish, making it unsuitable for human use.
Desalination plants can treat ocean water, as they do in the Middle East – or they can treat mineral groundwater, such as in El Paso!