Groundwater is like a big underground pool of water that we can't see because it's hidden under the ground. Sometimes things can happen that make the water in the pool dirty or unhealthy for people to use. This is called groundwater pollution.
So, imagine you have a big pool of water in your backyard. You and your friends like to swim in it during the summer. But one day, someone spills something like paint or chemicals on the ground near the pool. Those things can travel into the pool and make the water yucky. That's what happens with groundwater pollution, but on a bigger scale.
This pollution can come from a lot of different sources. For example, factories might dump waste into the ground, farms might use too many chemicals on their crops, or even the garbage we throw away can seep into the ground and pollute the groundwater.
The problem with groundwater pollution is that it can take a really long time to clean up. Because the water is hidden underground, it's much harder to get to and fix than polluted rivers or oceans. And since people rely on groundwater for drinking, bathing, and other things, it's really important that we try to keep it clean and healthy.
Overall, we need to be careful about what we do on land, so we don't accidentally pollute the hidden pool of water below us.