All pts in the hospital have a water seal. The water seal prevents back flow into the chest and it indicates if there is a leak. It is usually at the bottom of the collection system and the water is dyed blue. You can also look at the water seal chamber to see if there is fluctuation with respiration. It verifies the pressure variance with inhalation and exhalation. Unless, there is a specific collection system that doesn't have the seal (maybe some type of take home system), all CT systems have a water seal.
The confusion you are getting is the suction chamber. And the terms are either a dry suction water-seal or a wet suction water-seal system. It's not water seal vs dry suction. That's one half of two equations. Nurses sometimes don't specify the right terms. It's either dry suction or wet suction and they both have water seals.
This is a dry suction water seal. Notice the only water in the system is the water seal. It that chamber bubbles, there's a leak. There is no water suction chamber (wet). The dry suction systems have an orange plunger that pops out with suction and you can change the suction to -20 to -40 by turning the dial. So, there are only two chambers...the water seal and the collection chamber.
This a water seal, wet suction. Notice there are 3 chambers. The collection on the right, the water seal in the middle bottom and the suction chamber on the left. You change the -20 to -40 by how much water you fill on the left. Hence the term wet suction. That chamber will bubble depending on how much wall suction you provide. The water seal chamber shouldn't bubble unless there is a leak. Here's another wet suction....
Here is why a water seal is on all systems, regardless or wet suction or dry suction...
The middle stops air from back flowing and the right chamber offers pressure, while the first chamber catches drainage. Notice the tubes on the right are not submerged. If the water seal wasn't there, the air would love freely back and forth. The water seal ensures only one direction of air. It is the only submerged tube.
So, the terminology is very clear. You will need to know if the system is a wet suction water seal or a dry suction water seal. Then you will find out if the it is hooked up to suction or if it is to gravity. If it is to suction, find out how much suction is required...-20 h2O, -30 h20 or -40 h20. If the nurse says water seal or dry suction, that doesn't say anything.