What's wrong with the picture? Food and Harborage for Pests

This mop and dirty mop water were left in the facility overnight, as is. Thoughts?

Answer:

The dirty mop head and water provide an ideal place for drain gnats and other pests to breed and thrive.

The photos below show the resting drain gnats on the wall above the mop.

Taking a preventative approach is essential for effective pest control. Things become much more challenging once the pests have become established.