Plumbing System Basics: A Home Inspector’s Guide for Homeowners
Written by Mike S. Avelar, CPI
A home’s plumbing system delivers clean water, removes wastewater, and protects occupants from contamination. Understanding the basics helps homeowners recognize problems early and maintain a safe, efficient system. This guide covers water supply, piping materials, valves, hot water systems, drainage, venting, and common issues — all essential plumbing system basics every homeowner should know.
What Plumbing Systems Are Designed to Do
A properly designed plumbing system must:
- supply safe, potable hot and cold water
- deliver adequate pressure
- remove wastewater efficiently
- prevent contamination of drinking water
- protect occupants from sewer gases
As home inspectors, our priority is ensuring the system is safe, functional, and compliant with modern standards.
Water Supply: How Water Gets to Your Home
Municipal Water
Urban homes typically receive water from a municipal supply through underground service piping.
Wells
Rural homes often rely on drilled or dug wells. A pump delivers water through service piping into the home.
Service Piping Requirements
- buried below the frost line (approx. 1.22 m in Ottawa)
- minimal bends and elbows to maintain pressure
- modern urban service lines: ¾” pipe, approx. 40 psi
Improper Materials You Should NOT See
- cement or concrete joints
- glued joints between incompatible plastics
- female‑threaded PVC fittings
Shutoff Valves on the Water Supply Line
Several valves control water flow before it enters the home:
Corporation Stop
- located under the road
- used during construction or emergencies
- difficult to access
Curb Stop
- easier to access
- used for nonpayment shutoffs or basement flooding
Meter Stops
- two valves isolating the water meter
- allow maintenance or replacement
- can wear out if used too often
Hot and Cold Water Distribution Inside the Home
Once water enters the home, it travels through a network of pipes to fixtures.
General Layout
- hot water tank centrally located
- hot and cold risers branching to fixtures
- pipes suspended neatly with proper hangers
- risers must not rely on mains for support
Lead Solder in Older Homes
Centennial homes may have copper pipes joined with lead solder. Recommendation: Have your water tested and take action if lead levels are high.
Hot and Cold Pipe Separation
Hot and cold lines should be 6 inches apart unless hot lines are insulated.
Homes Without Basements
Water lines may run through crawlspaces, slabs, or even attics — the latter increases risk of freezing, condensation, and interior damage from leaks.
Common Plumbing Pipe Materials
PVC (Polyvinyl Chloride)
- used for sprinkler systems, pools, low‑pressure drains, and service lines
- durable but has potential health hazards
- More info: PVC Health Hazards by Nick Gromicko, CMI®
CPVC (Chlorinated PVC)
- yellow in colour
- suitable for hot and cold potable water
- good for corrosive water conditions
Copper
- durable and widely used
- should not be used if water pH ≤ 6.5 without treatment
- Grades:
- M (thin wall, interior use)
- L (thicker, exterior hose bibs)
- K (thickest, water mains)
Galvanized Steel
- lifespan ~40 years
- corrodes easily, restricting flow
- mismatched metals accelerate corrosion
- corrosion can interrupt electrical grounding
PEX (Cross‑linked Polyethylene)
- excellent for new builds and replacements
- flexible and freeze‑resistant (not freeze‑proof)
- ideal for corrosive water conditions
Kitec®
- used 1990–2005
- recalled due to rapid corrosion and leaks
Poly
- used mainly for cold water
- prone to cracking and clamp corrosion
Polybutylene (PB)
- used 1978–1995
- reacts with water treatment chemicals
- flakes and bursts over time
Plumbing Valves: What They Do and Where You’ll Find Them
Valves allow safe control of water flow throughout the system.
Shutoff Valves
- isolate sections for maintenance
- may be ball or gate valves
Check Valves
- allow water to flow in only one direction
Flow Control Valves
- maintain uniform flow at variable pressures
Relief Valves
- release excess pressure
Pressure‑Reducing Valves
- lower pressure on main lines
- allow use of thinner piping
Altitude Valves
- prevent hot water tanks from overflowing
Foot Valves
installed in wells to prevent backflow and loss of prime
Frost‑Proof Hose Bibs
- valve located inside the home
- operating handle outside
- prevents freezing
Frost‑Proof Hydrants
- shutoff valve buried below frost line
- may be prohibited due to contamination risk
Float Valves
- found in toilets and sump pumps
- open or close based on water level
Switches Used in Plumbing
- float switches
- pressure switches
- low‑flow cut‑off
- high‑pressure cut‑off
- paddle‑type switches
These devices help prevent contamination and maintain safe operation.
Heating Water: Tanks and Tankless Systems
Hot Water Tanks
Fuel sources include electricity, natural gas, fuel oil, or solid fuels.
All tanks must have a temperature‑pressure relief (TPR) valve with a discharge pipe ending no more than 6 inches above the floor.
If the TPR valve is releasing water, contact a plumber or rental company immediately.
Tankless Water Heaters
- heat water only when needed
- longer lifespan
- easier to repair
- must be properly sized for household demand
Wastewater and Drainage Systems
Wastewater flows through the sanitary drainage system, which carries interior wastewater only.
Drain Pipe Materials
- cast iron
- copper
- vitrified clay
- plastic (ABS or PVC)
- rare cases: lead
In Ottawa, ABS is the standard.
Plumbing Traps
Traps create a water seal that blocks sewer gases.
- P‑Trap is the most common
- S‑Traps are rare and require proper venting
Venting System
Vents prevent siphoning of trap seals and allow drains to function properly.
Without venting, sewer gases can enter the home — some are toxic or explosive.
Water Quality Problems
Water chemistry affects plumbing materials. Low pH water corrodes copper pipes and may require treatment systems.
Understanding water quality helps prevent damage and maintain safe drinking water.
Final Thoughts
A home’s plumbing system is complex, but understanding these plumbing system basics helps homeowners maintain safety, efficiency, and long‑term reliability. Regular inspections, proper materials, and awareness of common issues can prevent costly repairs and protect your home.