"Confined water" refers to a body of water that is restricted or limited in size or access. It could be a small lake, a swimming pool, or any other enclosed area of water.
This allows the perfect conditions for confined water dive training which are never affected by the weather (as a training site at a beach would be). (aqua-marina.com)
You'll apply the skills you learned in confined water while enjoying what the local environment has to offer. (padi.com)
This introductory discover scuba diving courses begins with confined water training in shallow water in the morning. (oahuscubadiving.com)