2 Section 1: Water Resources Some of the water we drink today has been around since water formed on Earth billions of years agoWater is essential to life on EarthHumans can only survive a for days without water
3 The Water CycleEarth has an abundance of water in all forms: solid, liquid, and gasWater is renewable because it gets circulated through the water cycle where water molecules travel between the surface and atmosphereWater vapor (a gas) rises into the airWater vapor cools as it rises through the atmosphere and condenses into droplets forming cloudsWater falls back down to Earth as precipitationOceans are an important part because so much of water on Earth is in the ocean
4 Global Water Distribution 71% of Earth's surface is covered with water, but 97% of water on Earth is salt waterOnly a small percentage is liquid, fresh water that humans can useIt is found in lakes, rivers, and beneath Earth's surface
5 Surface Water Surface water is fresh water on Earth's land surface It's found in lakes, rivers, streams, and wetlandsThroughout history, people have built cities near reliable sources of surface waterRivers, lakes, and streams provide drinking water, water to grow crops, food, power for industry, and transportation
6 River SystemsStreams form as water from falling rain and melting snow drains from mountains, hills, plateaus, and plainsAs streams flow downhill, they combine with other streams and form riversAs streams and rivers move across land, they form a flowing network of water called a river systemThe Mississippi, the Amazon, and the Nile are enormous river systemsThe Amazon is the largest river system in the world
7 Watersheds The area of land drained by the river is called a watershed Pollution anywhere in a watershed may end up polluting a riverThe amount of water entering a watershed changes throughout the yearRapidly melting snow, spring and summer rains, etc. can dramatically increase the amount of water in a watershedCommunities depending on these watersheds can be severely affected by changes in the river system
8 GroundwaterMost of the freshwater available to humans cannot be seen because it exists undergroundWater beneath Earth's surface in sediment and rock formations is called groundwaterThe point where rocks and soil are saturated with water is called the water tableThe water table can be at the surface or way below the surface
9 AquifersAn aquifer is an underground formation that contains groundwaterThe water table forms the upper boundary of an aquiferMost aquifers are rock, sand, and gravel that have lots of space for water to accumulateGroundwater can dissolve limestone rock formations filling vast caves with water creating underground lakesAquifers are an important water source for many cities and agriculture
10 Porosity and Permeability Although rocks appear to be solid, many kinds of rocks contain small holes or poresPorosity is the percentage of the total volume of a rock that has poresThe more porous a rock is, the more water it can holdThe ability of a rock or soil to allow water to flow through it is called permeabilityMaterials that allow water to flow through are permeable; materials that do not let water flow through are impermeable
11 WellsIf you go anywhere on Earth and dig a hole deep enough, you will eventually find water.A hole that is dug or drilled to reach groundwater is called a well.People dig wells because groundwater may be a more reliable source of water than surface water in some areas and because water is filtered and purified as it travels underground.
12 The Recharge ZoneTo reach an aquifer, surface water must travel down through permeable layers of soil and rockThe area of the Earth’s surface from which water percolates down into an aquifer is called a recharge zoneRecharge zones are environmentally sensitive areas because any pollution in a recharge zone can also enter the aquiferSize of recharge zone is affected by the permeability of the surface above the aquiferStructures such as buildings and parking lots can act as impermeable layers to reduce the amount of water entering an aquifer, so recharge zones must be managed carefully.
13 Copy now, answer laterDescribe the distribution of water on Earth. Where is most of the fresh water located?Explain why fresh water is considered a limited resource.Explain why pollution in a watershed poses a potential threat to the river system that flows through it.Describe how water travels through rock.Why is an underground lake an aquifer?