Freshwater use and conservation | Middle school Earth and space science | Khan Academy

本站添加: 2026-04-29

[00:00:01]It's a beautiful warm day and I'm taking my dog Rumble Thunderpaws for a walk. As we finish our usual hike coming down a rocky slope in eastern Tennessee, I give him some water to drink from a water bottle. But how do I know that my water is safe for him to drink? After all, only 2.5% of all the water on Earth is fresh water, and only a portion of that is safe to drink. The rest is salt water and isn't safe for us to drink. So, with only a tiny portion of all of our water on Earth being fresh water, how do we use it? Where does it go? And is it disappearing? And can we make more? So, first, let's think about how we use fresh water. You and I use fresh water every day. Whenever you brew a cup of tea or take a shower, you're using fresh water. Surprisingly, only 8% of our fresh water use goes to domestic purposes like cooking, cleaning, bathing, and drinking. or in the case when I fill my water bottle with tap water for a hike with good old Rumble Thunderpaws.

[00:01:05]In contrast though, the great majority or about 70% of global freshwater use goes to agriculture. And while that seems like a lot of water, and it is, this makes a bit of sense, too. We need to eat and we need water to grow food.

[00:01:22]And as populations increase, that means more people that need food and more food that we need to grow and of course more water that we need to use.

[00:01:34]Finally, about 22% of all fresh water worldwide goes to industrial uses, which includes electricity production, fossil fuel extraction, and manufacturing.

[00:01:44]Industries tend to use mainly fresh water because salt water corrods the metal parts used in machinery.

[00:01:51]Even though we use a lot of water, the amount of fresh water on Earth now is the same as there always has been. The only difference is that the population of humans has increased by leaps and bounds, meaning that there's more of us and more demand for fresh water. This figure shows how the human population has increased over time, in particular from the 1950s onwards. And this part of the figure shows estimates for the future human population. Keep in mind that as there's more of us, more people need fresh water. But with increased demand, there's just less available fresh water that's been treated and is safe to use. In many parts of the world, in particular in drier areas, freshwater sources are being used and drained faster than they are being replenished by rainwater or other sources. And there are other threats to fresh water, including pollution, agricultural runoff, habitat loss, and climate change. Let's take a closer look at one of these. Agricultural runoff puts excessive nutrients into surface waters that can cause harmful algaal blooms.

[00:02:56]This just goes to show just because water isn't salty doesn't mean it's fresh enough or clean enough for consumption. So if we have such a small amount of fresh water, why don't we treat salt water so we can drink it?

[00:03:10]Well, that's definitely possible. You can actually make fresh water from salt water through desalination, which removes the dissolved salts in salt water. Unfortunately, desalination processes are expensive, energyintensive, and involve large scale facilities. So, it's not a very accessible option right now. So, what else then can we do to conserve fresh water on Earth? Well, there's lots of things we can do. You can take shorter showers or turn off the tap while you're brushing your teeth. You can also get involved in your local community and check if there are initiatives or practices that reduce water use by businesses, industries, agriculture, and government. Let's do a quick summary.

[00:03:54]Fresh water is an incredibly important but limited resource. We use it for all kinds of things from bathing and drinking to growing food and producing electricity. Although we're not losing fresh water, sometimes we use fresh water faster than it is able to be replenished. But we can all do our part to conserve fresh water by making small changes to our everyday habits. What do you think, Rumble?

[00:04:19]>> Me, too. I know that you'd like shorter showers and bats for sure, buddy. And with that, I think I'll take Rumble out for a quick stroll around the neighborhood.