1. Warmup 2/29/16 You’ve all seen wells before. Where does the water come from? (not just “underground”) Objective Tonight’s Homework To learn about sources of fresh water underground p 401: 1, 3, 4, 6 p 404: 3

2. Groundwater Only 2.5% of the world’s water is drinkable. Of that 2.5%, only 1% is surface water. Most of the rest is in glaciers. But there’s 30 times more water soaked into the ground than in all the fresh lakes and rivers. However, it does NOT look like this and make giant underground lakes. Most just looks like wet rocks.

3. Groundwater Some rocks are a little like sponges. They can soak up and hold water. So if this water is 30 times more than in all the rivers and fresh lakes, where does it come from? If it rains for days, most of you notice that the ground becomes wet and squishy and stays that way. At this point, the ground is saturated with water.

4. Groundwater As time passes, this water soaks deeper into the ground. It keeps moving down until water fills all the cracks and pores between every little particle of rock. This process is called percolation. Eventually, it reaches an impermeable layer of rock that it can’t soak into. This is the bottom of the water table.

5. Groundwater Water tables are found under pretty much all the land of the earth. The only thing that varies is how deep you have to dig to get to the table and how deep the table itself is. If the ground dips low enough to go below the table, we get natural springs where water flows out of the ground on its own.

6. Groundwater The level of the water table varies depending on the season. In spring, it recharges, filling up with melting snow. In the fall it’s usually several meters lower. When we dig a well, we dig it deep enough to hit rocks that contain the water table. At this point, water naturally seeps from the rock into the well, where people can draw water from it.

7. Groundwater We have to remember that this isn’t a big lake of water. It’s water that’s soaked into stone. If you draw a lot of water from a well, the surrounding rock starts to dry up. This dry area is called a cone of depression. If a person draws enough water from a well, it can pull down the water table in the area and maybe even affect other nearby wells!

8. Groundwater Not all rocks can soak up water, though. We said that some are impermeable – water can’t go through them. If we have a layer of this rock above our water table, we can get a second, smaller water table above this layer. This is called a perched water table. If we have a layer of permeable rock between two layers of impermeable material, we have an aquifer. Aquifers are usually under pressure. If a well is drilled into one, water will rise up on its own.

9. Groundwater Most of the water in your house isn’t pure. Since water tables form inside rocks, they also can dissolve them a little. Most water contains some of these dissolved minerals. When talking about how much minerals a sample of water has, we use the term “hardness”.

10. Groundwater Hard water usually contains a lot of dissolved minerals. When the water dries, it usually leaves behind a thin film of these minerals that you can easily see. It’s usually calcium. Hard water generally tastes better and you need the minerals, but it’s not very good for cleaning. Hard water doesn’t make tons of suds when mixed with soap, so it can make getting soap off in the shower a bit difficult.

11. Groundwater Soft water doesn’t contain many minerals, but is better for cleaning and industry. Minerals in hard water can stick to pipes, causing the pipes to shrink and get blocked up. Fixing this is expensive, so most industrial areas work hard to make sure their water is soft.

12. 3 rd quarter notebook check Friday is the end of the third quarter. That means it’s time for Mr. C. to hand out notebook checklists again. Like before, this will be due Friday!

13. Exit Question What’s the difference between an aquifer and a water table? Aquifers are under pressure, water tables aren’t Water tables are under pressure, aquifers aren’t Aquifers are full of salt water, water tables aren’t Water tables are full of salt water, aquifers aren’t There is no difference. It’s different names for the same thing. None of the above