Each fixture trap shall have a water seal of not more than how many inches?

The correct answer highlights that each fixture trap must maintain a water seal of not more than 4 inches. This requirement is crucial because the water seal in a trap serves to prevent sewer gases from entering the living space, while still allowing wastewater to flow through. A water seal of up to 4 inches is considered effective in providing sufficient blockage against harmful gases while maintaining the necessary drainage function.

This dimension is established by plumbing codes to ensure a balance between effective gas sealing and the ease of drainage. A seal that is too shallow might not adequately prevent the escape of gases, while a deeper seal could lead to issues such as potential blockage or increased resistance to drainage flow. Thus, setting the maximum seal at 4 inches ensures both safety and functionality in plumbing systems.