Groundwater pollution has become a serious environmental problem.

We should recycle to prevent environmental pollution.

The underground water in this area is very clean and is used as drinking water.

This polluted water could potentially harm our health.

This problem is very serious.

Do you understand the seriousness of this problem?

We must strive to protect the environment of the Earth.

The subway is running underground.

I commute by subway.

The pollution in this area has become a serious problem.