Systems & Code
Plumbing Systems Overview & Code
The two main systems in every building and the purpose of the plumbing code.
The Two Main Systems
Every plumbing installation has two separate systems:
1. WATER SUPPLY (pressurized) — brings clean, potable water in under pressure to fixtures. 2. DRAIN-WASTE-VENT (DWV) (gravity) — carries wastewater out by gravity and vents sewer gases to the outside.
The golden rule of plumbing: protect the potable water supply from contamination, and keep the two systems from ever cross-connecting.
Purpose of the Code
Plumbing codes (such as the IPC or UPC, depending on your jurisdiction) exist to protect public health and safety — clean water in, waste safely out. They set minimum standards for materials, sizing, installation, and testing.
The code is a MINIMUM standard; local amendments can be stricter. Always follow the code adopted by your local jurisdiction.
Potable vs. Non-Potable
POTABLE water is safe to drink. NON-POTABLE water (e.g. greywater, irrigation) is not. The two must never connect in a way that lets non-potable water enter the potable supply — that's a CROSS-CONNECTION, and preventing it is the heart of plumbing safety.
📖 Key Terms
- Potable water
- Water that is safe for human consumption.
- DWV
- Drain-Waste-Vent — the gravity system that removes wastewater and vents gases.
- Cross-connection
- Any link that could allow non-potable water to enter the potable supply.
- Code minimum
- The least the code allows; local rules may be stricter.
💡 Exam Tips
- ▸Two systems: pressurized water supply IN, gravity DWV OUT.
- ▸The code's #1 goal is protecting potable water from contamination.
- ▸A cross-connection is any path for non-potable water to enter the potable supply.
- ▸Code is a minimum — local amendments can be more stringent.