Water drainage for an entire household, regardless if it is shower water or kitchen sink water, all end up in the common sewage system exiting the property. Proper plumbing piping protects both the home's plumbing and the environment.
Regulations stipulate that all shower drains, as well as all fixtures applied to the common plumbing system of a building, need P-traps. A P-trap is the curved pipe seen under a bathroom or kitchen sink directing waste water back into the wall. This same piping is used under the shower drain.
P-traps are utilized to provide a barrier for sewage fumes and small organisms to enter the building. They are also useful in case of accidental item drops down the drain. The P-trap is a way to divide the fixture from the external plumbing, allowing rescue of the item before it is washed away.
The barrier within the P-trap to prevent fumes is trapped water from using the faucet or shower.