The New York City subway is a very important system for travel. Many people use the trains every day. But this system is very old. Because it is old, it has a big problem.
The problem is water. When it rains a lot, water gets into the subway stations. The tunnels under the ground can fill with water. This is not safe for the trains or the people.
When there is too much water, the trains must stop. This makes travel very hard for everyone. People are late for work and school. Fixing this is a big job for the city.