Water seal drainage system is a closed chest drainage system used to allow air and fluid to escape from the pleural space with each exhalation. Drainage systems are placed to remove the excess water in building development.
There are also drainage systems that are put in place to eradicate wastewater effectively, and this is referred to as a sewer system — not having the proper drainage system in place will result in flooding. An adequate drainage system removes all excess water without flooding.
It allows air to exit the pleural space but prevent air from entering the pleural space through the chest tube
The water seal acts as a one-way valve: it allows air to exit through the system while preventing air from re-entering the pleural space, which could lead to accumulation of a pneumothorax. Losing the water seal would cause the same problem as having the creech tubing and thoracic catheter become disconnected and the thoracic catheter end open to the air.