As is the case for solutions, the name might seem odd but many. if not most, preparation of gases involves the use of aqueous solutions.
As a result, the gases generated are mixed with varying amounts of water vapiur, depending on the temperature and amount of effervescence.
In most cases this is of no importance but some procedures are very sensitive to the presence of seven small amounts of water.
It is important to select the right drying agent as some will react with the gas being produced. Details of methods and of various drying agents can be found here.