In the short story 'The Last Night of the World' by Ray Bradbury, why did the wife leave the water of the kitchen sink on?

When they were in bed together, the wife suddenly said she had left the tap running in the sink.This had happened because she was washing up at the time when her husband had said about the dream that everybody had had about the last night of the world. They were all resigned to the fact that this was going to be everybody's last night, so turning off the tap was in fact pointless.